Add mTLS authentication

[sehkone]

Closes #768

[codecov]

Codecov Report

❌ Patch coverage is 77.00535% with 86 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.74%. Comparing base (b2fde00) to head (3209eef).
⚠️ Report is 1 commits behind head on auth-mtls.

Files with missing lines	Patch %	Lines
src/lib.rs	64.73%	61 Missing ⚠️
src/auth/mtls.rs	88.08%	23 Missing ⚠️
src/graphql/cert.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           auth-mtls     #769      +/-   ##
=============================================
+ Coverage      73.04%   73.74%   +0.70%     
=============================================
  Files             70       71       +1     
  Lines          17708    18068     +360     
=============================================
+ Hits           12934    13324     +390     
+ Misses          4774     4744      -30     

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