Add debug message for cluster unreachable at plan time

[jrhouston]

The CustomizeDiffFunc function doesn't allow us to surface diagnostic messages when something goes wrong, only errors.

We don't want the plan to fail so instead we mark "manifest" as computed and swallow the error, and write a debug log.

Description

Acceptance tests

• Have you added an acceptance test for the functionality being added?

Release Note

Release note for CHANGELOG:

...

References

Community Note

• Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritize this request
• If you are interested in working on this issue or have submitted a pull request, please leave a comment

[alexsomesan]

Seems legit

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.