CLI: Make --force deprecation print on stderr

[keraion]

Brief summary of the change made

Removes the deprecation warning from stdout and puts it on stderr. Before, the output would be included in the output file if piping to a file.

fixes #5679

Are there any other side effects of this change that we should be aware of?

None

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[github-actions]

Coverage Results ✅

Name    Stmts   Miss  Cover   Missing
-------------------------------------
TOTAL   17337      0   100%

225 files skipped due to complete coverage.

[coveralls]

coverage: 99.984%. remained the same
when pulling a122d35 on keraion:force_deprecation_stderr
into 5b39b51 on sqlfluff:main.

[WittierDinosaur]

LGTM