[Core] Add content to v1.9 upgrade guide for beta

[mirnawong1]

Link to the page(s) on docs.getdbt.com requiring updates

Add any relevant content to v1.9 upgrade guide for upcoming beta

Tell us more about this update

Please use the following template as guidance (@matthewshaver will have more info): https://docs.getdbt.com/docs/dbt-versions/core-upgrade/upgrading-to-v1.8

Reviewers/Stakeholders/SMEs

@graciegoheen
@jtcohen6

Related GitHub issues

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Additional information

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[graciegoheen]

Now that adapters are decoupled from core.. should the 1.9 guide only focus on new "core" features (microbatch, snapshot improvements, etc.) or should it include "adapter" features still also (iceberg table format, etc.)?

cc: @jtcohen6

[graciegoheen]

My very rough thoughts on what should go in this! (cc: @dbeatty10 @jtcohen6)

Big features to highlight:

• new microbatch incremental_strategy
  • new supporting configs (event_time, begin, lookback, batch_size
• improvements to snapshots
  • new snapshot spec (define in yml)
  • new snapshot_meta_column_names config for customizing name of meta fields
  • target_schema is now optional for snapshots - omit for environment-aware snapshots
  • add standard schema/database configs for snapshots
  • warning when updated_at is not proper data type / timestamp
  • [maybe] new way to track deletes (config etc.)
• [maybe] less false positives in state:modified
  • state_modified_compare_more_unrendered_values
  • state_modified_compare_vars

Small wins:

• can now add descriptions to singular data tests
• can use ref and source in foreign key constraints
• can use --exclude-resource-type + associated environment variable (and "include" opposites --resource-type) in dbt test command (for excluding unit tests in production)
• new --inline-direct parameter for 'dbt show'
• [adapters] data_test accepts arbitrary config options (allows you to set snowflake_warehouse for tests, as an example)
• [adapters] behavior flags

Other callouts:

• a reminder for Cloud folks to use versionless to get access to these new features
• a reminder that adapters have been decoupled with core (implications for installation)
• behavior change flag callouts!
• check with semantic layer team if there's anything to add! (time spines?) @Jstein77
• check with adapters team if there's anything to add! @amychen1776