sql: support in-place storage shrink for google_sql_database_instance

[DrFaust92]

Summary

Reducing disk_size on google_sql_database_instance (with disk_autoresize disabled) previously forced the instance to be recreated — a destructive operation for a data disk. Cloud SQL now supports reducing storage in place via the dedicated Instances.PerformDiskShrink operation (GA for MySQL/PostgreSQL, and available for SQL Server).

This change wires that up:

• diskSizeCutomizeDiff no longer calls ForceNew on a shrink; the shrink is kept as an in-place update.
• On update, a disk_size decrease is carried out with Projects.Instances.PerformDiskShrink (the settings update keeps the current size, so it's a no-op for disk).
• A pre-flight GetDiskShrinkConfig call returns a clear error when the requested size is below the instance's current minimum shrinkable size, instead of letting the shrink operation start and then fail.
• disk_size field docs updated.

Increases are unaffected (still applied via the settings update). A shrink with disk_autoresize enabled continues to be ignored, as before.

Tests

Acceptance tests were run against real GCP:

• TestAccSqlDatabaseInstance_storageShrink (new) — creates a 100GB instance and shrinks it in place to 90GB, asserting the disk size and that the instance is not recreated (same ID). PASS
• TestAccSqlDatabaseInstance_DiskSizeAutoResizeWithDiskSize (updated) — the step that previously asserted a forced recreate now asserts an in-place update plan (PlanOnly + ExpectNonEmptyPlan). PASS

Note: storage shrink is not supported on shared-core machine types, so the new test uses a db-custom-* tier.

Release Note

sql: `google_sql_database_instance` now performs an in-place storage shrink when `disk_size` is reduced with `disk_autoresize` disabled, instead of forcing instance recreation

[github-actions]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit ef335c3:

Diff report

Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
google provider	View Diff	2 files changed, 138 insertions(+), 19 deletions(-)
google-beta provider	View Diff	2 files changed, 138 insertions(+), 19 deletions(-)

Test report

Analytics

Total Tests	Passed	Skipped	Affected
163	132	30	1

Affected Service Packages

• sql

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Step 1: Replaying Mode

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit.

Click here to see the affected tests

• TestAccSqlDatabaseInstance_storageShrink

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Step 2: Recording Mode

Recording Mode	Replaying Rerun	Test Name
✅ Log	✅	TestAccSqlDatabaseInstance_storageShrink

🟢 All tests passed!

View the recording VCR build log or the debug logs folder for detailed results.

@DrFaust92, @shuyama1 VCR tests complete for ef335c3!