[Vibe-coded] Add skip_validation attribute to kubernetes_manifest resource

[a0s]

• Add skip_validation boolean attribute to resource schema
• Skip cluster connection and validation during plan phase when enabled
• Add documentation with usage examples
• Update 'Before you use this resource' section

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

Description

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccXXX'

...

Release Note

Release note for CHANGELOG:

...

References

Community Note

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