Adding multiple unique keys (#6438)

Closes #6343

## What are you changing in this pull request and why?

Adds multiple unique keys as outline in [this
plan](#6343 (comment)).

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<!-- vercel-deployment-preview -->
---
🚀 Deployment available! Here are the direct links to the updated files:


-
https://docs-getdbt-com-git-mult-unique-keys-dbt-labs.vercel.app/docs/build/snapshots
-
https://docs-getdbt-com-git-mult-unique-keys-dbt-labs.vercel.app/reference/resource-configs/unique_key

<!-- end-vercel-deployment-preview -->

---------

Co-authored-by: Mirna Wong <[email protected]>

website/docs/docs/build/snapshots.md

@@ -83,7 +83,7 @@ The following table outlines the configurations available for snapshots:
 | [schema](/reference/resource-configs/schema) | Specify a custom schema for the snapshot | No | snapshots |
 | [alias](/reference/resource-configs/alias)   | Specify an alias for the snapshot | No | your_custom_snapshot |
 | [strategy](/reference/resource-configs/strategy) | The snapshot strategy to use. Valid values: `timestamp` or `check` | Yes | timestamp |
-| [unique_key](/reference/resource-configs/unique_key) | A <Term id="primary-key" /> column or expression for the record | Yes | id |
+| [unique_key](/reference/resource-configs/unique_key) | A <Term id="primary-key" /> column(s) (string or array) or expression for the record | Yes |  `id` or `[order_id, product_id]` |
 | [check_cols](/reference/resource-configs/check_cols) | If using the `check` strategy, then the columns to check | Only if using the `check` strategy | ["status"] |
 | [updated_at](/reference/resource-configs/updated_at) | If using the `timestamp` strategy, the timestamp column to compare | Only if using the `timestamp` strategy | updated_at |
 | [invalidate_hard_deletes](/reference/resource-configs/invalidate_hard_deletes) | Find hard deleted records in source and set `dbt_valid_to` to current time if the record no longer exists | No | True |

website/docs/reference/resource-configs/unique_key.md

@@ -1,6 +1,6 @@
 ---
 resource_types: [snapshots]
-description: "Unique_key - Read this in-depth guide to learn about configurations in dbt."
+description: "Learn more about unique_key configurations in dbt."
 datatype: column_name_or_expression
 ---
 
@@ -14,7 +14,7 @@ snapshots:
   - name: orders_snapshot
     relation: source('my_source', 'my_table')
     [config](/reference/snapshot-configs):
-      unique_key: id
+      unique_key: order_id
 
 ```
 
@@ -52,7 +52,7 @@ snapshots:
 ## Description
 A column name or expression that is unique for the inputs of a snapshot. dbt uses this to match records between a result set and an existing snapshot, so that changes can be captured correctly.
 
-In Versionless and dbt v1.9 and later, [snapshots](/docs/build/snapshots) are defined and configured in YAML files within your `snapshots/` directory. The `unique_key` is specified within the `config` block of your snapshot YAML file.
+In Versionless and dbt v1.9 and later, [snapshots](/docs/build/snapshots) are defined and configured in YAML files within your `snapshots/` directory. You can specify one or multiple `unique_key` values within your snapshot YAML file's `config` key.
 
 :::caution 
 
@@ -114,29 +114,37 @@ snapshots:
 
 </File>
 
-### Use a combination of two columns as a unique key
-This configuration accepts a valid column expression. As such, you can concatenate two columns together as a unique key if required. It's a good idea to use a separator (e.g. `'-'`) to ensure uniqueness.
-
 <VersionBlock firstVersion="1.9">
 
+### Use multiple unique keys
+
+You can configure snapshots to use multiple unique keys for `primary_key` columns.
+
 <File name='snapshots/transaction_items_snapshot.yml'>
 
 ```yaml
 snapshots:
-  - name: transaction_items_snapshot
-    relation: source('erp', 'transactions')
+  - name: orders_snapshot
+    relation: source('jaffle_shop', 'orders')
     config:
       schema: snapshots
-      unique_key: "transaction_id || '-' || line_item_id"
+      unique_key: 
+        - order_id
+        - product_id
       strategy: timestamp
       updated_at: updated_at
-
+      
 ```
+
 </File>
 </VersionBlock>
 
 <VersionBlock lastVersion="1.8">
 
+### Use a combination of two columns as a unique key
+
+This configuration accepts a valid column expression. As such, you can concatenate two columns together as a unique key if required. It's a good idea to use a separator (for example, `'-'`) to ensure uniqueness.
+
 <File name='snapshots/transaction_items_snapshot.sql'>
 
 ```jinja2
@@ -159,25 +167,9 @@ from {{ source('erp', 'transactions') }}
 ```
 
 </File>
-</VersionBlock>
 
 Though, it's probably a better idea to construct this column in your query and use that as the `unique_key`:
 
-<VersionBlock firstVersion="1.9">
-
-<File name='snapshots/transaction_items_snapshot.yml'>
-
-```yaml
-snapshots:
-  - name: transaction_items_snapshot
-    relation: {{ ref('transaction_items_ephemeral') }}
-    config:
-      schema: snapshots
-      unique_key: id
-      strategy: timestamp
-      updated_at: updated_at
-```
-</File>
 
 <File name='models/transaction_items_ephemeral.sql'>
 
@@ -195,9 +187,6 @@ from {{ source('erp', 'transactions') }}
 
 In this example, we create an ephemeral model `transaction_items_ephemeral` that creates an `id` column that can be used as the `unique_key` our snapshot configuration.
 
-</VersionBlock>
-
-<VersionBlock lastVersion="1.8">
 <File name='snapshots/transaction_items_snapshot.sql'>
 
 ```jinja2