SRE-2560 Fix CDKTF Diff Output

[jadabyte256]

Closes snapsheettech.atlassian.net/browse/SRE-2560

What

Changes the jobs for writing the output/result to always run even if the diff fails and updates logic for determining whether a diff succeeded to prevent the issue when a plan is created, but the underlying diff command fails due to a data lookup failure (this was seen when the serverless DB cluster was not supported by the cdtkf-infra version).

Why

Previously, if one of the cdktf-diff matrix jobs failed, it would skip the output and no summary would be printed out. This makes it tedious to copy plan links into PRs for review. Additionally, the action would succeed in cases where an actual plan was generated even though the command returned a non-success exit code, which could potentially hide failures from teams in certain scenarios.

How

• Adds additional output parsing and exit code checks.
• Makes artifact upload run always so failures produce output in the summary.

Testing

You may run the cdktf-diff action in vice-backend using the workflow from SRE-2560-fix-cdktf-diff-output to test.

Example tests:

• Failure from Serverless DB Dashboard - verify that vice-backend-release actually shows a failure for the ref diff.
• State locked - verify that vice-backend-qa8 failed in both diffs. If you'd like to test this, run a locally apply and do not accept the plan - just let it set at the prompt so that the state is locked and run the action.