[FLINK-30400][docs] Add some notes about changes for flink-connector-base dependency in externalized connectors

[ruanhang1993]

What is the purpose of the change

This pull request adds some notes about changes for flink-connector-base dependency in externalized connectors.

Brief change log

Add some notes about changes for flink-connector-base dependency in externalized connectors docs.

Verifying this change

This change is a docs work without any test coverage.

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)

[ruanhang1993]

@rmetzger @leonardBang Would you like to help to review this PR?

[flinkbot]

CI report:

• ace19bbeee9cc5e5f8ecf784aa3ed5e55d073f7f Azure: SUCCESS
• eaee3c4cb91ad5e01daa75e886c78b0fe119f4c1 Azure: PENDING

Bot commands

The @flinkbot bot supports the following commands:

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

[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If this PR is no longer valid or desired, please feel free to close it.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 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If this PR is no longer valid or desired, please feel free to close it.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.

[leonardBang]

@ruanhang1993 Sorry for late reply, but I think this PR still has meaning for users, could you update this PR to latest master branch ?