Finish missing sources from Datastream Stream

[modular-magician]

PR Description

Add missing fields and behavior from recently implemented Datastream Stream resource GoogleCloudPlatform/magic-modules#6806

Changes:

1. Add Postgres & Oracle source configs
2. Call an additional update after create stream if the desired_state was RUNNING.
3. Add support for validation results in operation errors

This PR was re created after GoogleCloudPlatform/magic-modules#7115 was accidentally deleted

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

datastream: Added `postgresql_source_config` & `oracle_source_config` in `google_datastream_stream`

datastream: Added support for `desired_state=RUNNING` in `google_datastream_stream`

datastream: Exposed validation errors in `google_datastream_stream`

Derived from GoogleCloudPlatform/magic-modules#7175