[FLINK-36008][Documentation] Script and guidance to preview connector docs contributions

[nicusX]

What is the purpose of the change

• Improving the contributors' experience when modifying docs of an existing connector or developing docs of a new connector.

Brief change log

• Add a function to docs/setup_docs.sh script that can be used to import a fork of a connector repo
• Add instructions to docs/README.md about generating docs locally to preview your connector's docs contribution

TL;DR

To generate the docs site locally including the docs of the connector you are working on (while your changes are still in a fork, and not yet merged into the main connector repo) you need to edit the setup_docs.sh pointing to your form, and then you can generate the site.

I added a function in setup_docs.sh that you can use for this. The original integrate_connector_docs function only works with merged connectors. I preferred not to touch it.

Verifying this change

The change can be verified generating the docs site, locally, following the new additional instructions in docs/README.md:

1. Have Hugo installed
2. Have a fork of a connector repo
3. Push any docs change to a branch/tag
4. Modify docs/setup_docs.sh replacing the existing integrate_connector_docs ... with integrate_connector_fork_docs <fork-owner> <connector-name> <branch-name> (e.g. integrate_connector_fork_docs nicusX prometheus FLINK-33137-docs)
5. Run setup_docs.sh and then build_docs.sh normally
6. Verify the changes in your fork are visible

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): No
• The public API, i.e., is any changed class annotated with @Public(Evolving): No
• The serializers: No
• The runtime per-record code paths (performance sensitive): No
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: No
• The S3 file system connector: No

Documentation

• Does this pull request introduce a new feature? No
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 2623c73427a81161cf03ed7ec2f66724a2bcd385 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[nicusX]

@dannycranmer I rephrased the whole explanation, being more explicit, considering it was not clear which repo we were talking about. Let me know if it makes sense now

[github-actions[bot]]

This PR is being marked as stale since it has not had any activity in the last 90 days. If you would like to keep this PR alive, please leave a comment asking for a review. If the PR has merge conflicts, update it with the latest from the base branch.

If you are having difficulty finding a reviewer, please reach out to the community, contact details can be found here: https://flink.apache.org/what-is-flink/community/

If this PR is no longer valid or desired, please feel free to close it. If no activity occurs in the next 30 days, it will be automatically closed.

[github-actions[bot]]

This PR has been closed since it has not had any activity in 120 days. If you feel like this was a mistake, or you would like to continue working on it, please feel free to re-open the PR and ask for a review.

[nicusX]

@dannycranmer this PR was closed for inactivity, but I think it was mergeable. The instructions suggest to re-open it but I do not have the permissions. It think this would be a useful addition to help anyone who is updating connectors doc