[DOCS]Remove duplicate faq page

[bhasudha]

There are two faq.md files. Both mostly same except for minor divergence.
Removing learn/faq.md and redirecting all faq links to docs/faq.md which will
be the one source of truth going forward.

Tips

• Thank you very much for contributing to Apache Hudi.
• Please review https://hudi.apache.org/contribute/how-to-contribute before opening a pull request.

What is the purpose of the pull request

(For example: This pull request adds quick-start document.)

Brief change log

(for example:)

• Modify AnnotationLocation checkstyle rule in checkstyle.xml

Verify this pull request

(Please pick either of the following options)

This pull request is a trivial rework / code cleanup without any test coverage.

(or)

This pull request is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end.
• Added HoodieClientWriteTest to verify the change.
• Manually verified the change by running a job locally.

Committer checklist

• Has a corresponding JIRA in PR title & commit

• Commit message is descriptive of the change

• CI is green

• Necessary doc changes done or have another open PR

• For large changes, please consider breaking it into sub-tasks under an umbrella JIRA.