[3007.x] [DOCS] Refresh gitfs/git_pillar/s3fs/file_roots docs

[dwoz]

Summary

Refresh of the gitfs / git_pillar / s3fs / file_roots docs to address five
long-standing documentation issues:

• [DOCS] gitfs walkthrough references out of date dependencies #62260 gitfs walkthrough: drops EOL distro notes (Ubuntu 14, Debian
  Wheezy, RHEL/CentOS 7.3-era CFFI quirks) and pins the recommended
  dependency versions to what requirements/base.txt and the CI lockfiles
  already require (pygit2 >= 1.13.1 / >= 1.19.2 on py3.11+, GitPython
  >= 3.1.50). Salts internal GITPYTHON_MINVER / PYGIT2_MINVER floors
  are unchanged.
• external git pillar docs ref incorrect #56127 git_pillar external pillar: enumerates the supported remote
  URL forms (https, ssh://, scp-style user@host:path, file://) and calls
  out the scp-style colon as the most common source of "Failed to resolve
  address" / "Unable to exchange encryption keys" errors at master start.
• [DOCS] Adding gitlab config info in GIT FILESERVER BACKEND WALKTHROUGH #60809 GitLab support: new "GitLab" subsection in the Authentication
  section of the walkthrough covering deploy tokens, project access
  tokens, personal access tokens, and SSH deploy keys, plus the 401
  failure mode for expired or under-scoped tokens.
• [DOCS] please document that s3fs may require setting regional s3 endpoint #60408 s3fs regional endpoint: new "Regional endpoints" section in
  the s3fs.py module docstring documenting s3.location,
  s3.service_url, s3.https_enable, s3.path_style, and s3.verify_ssl
  with the SigV4 redirect failure mode.
• salt docs recommending file_roots change? #53746 file_roots location: new "Where should file_roots live?"
  section explaining the /srv/salt default. Updates the
  netconfig.managed and napalm_network docstring examples to use
  /srv/salt so the inline example matches the recommendation.

Test plan

• sphinx-build -W --keep-going -b html clean (no new warnings)
• sphinx-build -W --keep-going -b man clean
• pre-commit run on all modified files
• pytest tests/pytests/functional/fileserver/gitfs/test_documented_providers.py (7 passed)
• pytest tests/pytests/unit/fileserver/test_s3fs_documented_options.py (6 passed) — 3006.x / 3007.x only

Closes #62260
Closes #56127
Closes #60809
Closes #60408
Closes #53746