[KYUUBI #7434][DOC] Reformat client docs from RST to Markdown

[dnskr]

Why are the changes needed?

The changes are needed to unify the format used for documentation, as described in the issue #7434.

The PR also:

• Removes empty pages:
  • docs/client/advanced/configurations.rst
  • docs/client/advanced/features/engine_resources.rst
  • docs/client/advanced/features/engine_share_level.rst
  • docs/client/advanced/features/engine_ttl.rst
  • docs/client/advanced/features/engine_type.rst
  • docs/client/advanced/features/scala.rst
  • docs/client/advanced/logging.rst
• Simplifies Client Commons menu: remove features directory and move Plan Only Execution Mode page up.
• Increases myst_heading_anchors to 4 to fix the following warning:

  ./docs/client/rest/rest_api.md:281: WARNING: 'myst' cross-reference target not found: 'kyuubioperationevent' [myst.xref_missing]
  

• Rename Configure Kerberos for clients to Access Kerberized Kyuubi to Kerberos Configuration and remove the page from Security / Authentication index page.
• Fixed cross-references.

The PR does not change page contents to ensure an easier review of the migration.

How was this patch tested?

Tested by building the documentation and comparing the pages against the live site.

Was this patch assisted by generative AI tooling?

Assisted-by: Qwen Coder