feat: add cluster datasource and cluster resource import

[dimitarproynov]

Summary of Pull Request

Extract the Import Method into cluster_operations.go for reuse. Add more "flatten" functions since, the import operation should provide the user with more info, than the cluster::read, which operates on the premise that the user has already provided the data needed to create a cluster.

Type of Pull Request

• [ ] This is a bug fix.
• [X] This is an enhancement or feature.
• [ ] This is a code style/formatting update.
• [X] This is a documentation update.
• [X] This is a refactoring update.
• [ ] This is a chore update
• [ ] This is something else. Please describe:

Related to Existing Issues

Closes #33 Closes #34

Test and Documentation Coverage

For bug fixes or features:

• [x] Tests have been completed.
• [X] Documentation has been added/updated.

Breaking Changes?

• [ ] Yes, there are breaking changes.
• [X] No, there are no breaking changes.

[pandeyhere]

Looks good to me

[github-actions[bot]]

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