fix: added variable validation to var.rotation_interval_month

[ocofaigh]

Description

• fix: added variable validation to var.rotation_interval_month to only allow value between 1 and 12.
• documentation and variable description cleanup
• updated the default example to use ibm_resource_instance to provision the KP instance instead of the terraform-ibm-key-protect module since it also requires restapi provider (Had to skip upgrade test for this - no impact to main module)
• test cleanup (removed code duplication)

Check the relevant boxes:

• Bug fix (nonbreaking change that fixes an issue)
• New feature (nonbreaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Examples or tests (addition or updates of examples or tests)
• Documentation update
• CI related update (pipeline, etc.)

Checklist

• If relevant, a test for the change has been added or updated as part of this PR.
• If relevant, documentation for the change has been added or updated as part of this PR.

Merge

• Merge using "Squash and merge".
• Make sure to use a relevant conventional commit message that is based on the PR contents. The commit message determines whether a new version of the modules needs to be released, and if so, which semver number to use).

[MatthewLemmond]

One small change, everything looks good otherwise

[terraform-ibm-modules-ops]

🎉 This PR is included in version 1.0.2 🎉

The release is available on GitHub release

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