fix helm notifications config

[dyu-bot]

Tracking issue

Closes #3070

Describe your changes

• Remove deprecated region field in NotificationsConfig
• Sets cloud provider config depending on which provider type is specified. This is needed in order for cloud-based notifications to work (guessing it's blocked now for both GCP and AWS). See this issue.

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Screenshots

I tested the latest flyteadmin v1.1.129 using flyte-core chart running on GKE v1.26 with these configs:

  workflow_notifications:
    enabled: true
    config:
      notifications:
        type: gcp
        gcp:
          projectId: xxx
        publisher:
          topicName: "xxx"
        processor:
          queueName: "xxx"
        emailer:
          emailServerConfig:
            serviceName: sendgrid
            apiKeyEnvVar: xxx
          subject: "Notice: Execution \"{{ workflow.name }}\" has {{ phase }} in \"{{ domain }}\"."
          sender:  "xxx"
          body: >
             Execution \"{{ workflow.name }} [{{ name }}]\" has {{ phase }} in \"{{ domain }}\". View details at
             <a href=\https://xxx.com/console/projects/{{ project }}/domains/{{ domain }}/executions/{{ name }}>
             https://xxx.com/console/projects/{{ project }}/domains/{{ domain }}/executions/{{ name }}</a>. {{ error }}

And observe the correct notifications config passed to flyte-admin-base-config configmap

Flyteadmin is able to run successfully.

Note to reviewers

Note: I have not tested this on AWS as I do not have easy access (if someone could that would be great!)

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