Add SSH public key authentication

[sparsick]

Git clone is now possible with a Public key authentication.

[codecov]

Codecov Report

Patch coverage: 93.10% and project coverage change: +0.78% 🎉

Comparison is base (0223d0c) 91.66% compared to head (42aae13) 92.45%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #17      +/-   ##
============================================
+ Coverage     91.66%   92.45%   +0.78%     
- Complexity        9       18       +9     
============================================
  Files             1        3       +2     
  Lines            24       53      +29     
  Branches          2        2              
============================================
+ Hits             22       49      +27     
- Misses            2        4       +2     

Files Changed	Coverage Δ
...k/testcontainers/gitserver/GitServerContainer.java	88.57% <81.81%> (-3.10%)	⬇️
...ck/testcontainers/gitserver/GitServerVersions.java	100.00% <100.00%> (ø)
...sparsick/testcontainers/gitserver/SshIdentity.java	100.00% <100.00%> (ø)

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