feat: mTLS support

[rustatian]

Reason for This PR

closes: roadrunner-server/roadrunner#1300

Description of Changes

• Add mTLS support.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.

[codecov-commenter]

Codecov Report

Merging #274 (1855ff9) into master (4892aae) will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master    #274      +/-   ##
=========================================
- Coverage    3.24%   3.12%   -0.13%     
=========================================
  Files          15      15              
  Lines        1480    1538      +58     
=========================================
  Hits           48      48              
- Misses       1430    1488      +58     
  Partials        2       2              

Impacted Files	Coverage Δ
config.go	0.00% <0.00%> (ø)
plugin.go	0.00% <0.00%> (ø)

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