Allow self-signed ca certs with EcDSA and Ed25519

[cviecco]

The current implementation only worked for P-256 and rsa keys, because we had a harcoded hash type. Makes the hash type dependent on the publicKey (which is derived from the public one).

[codecov]

Codecov Report

Attention: Patch coverage is 59.09091% with 9 lines in your changes missing coverage. Please review.

Project coverage is 32.17%. Comparing base (efb227d) to head (ff06b61).

Files	Patch %	Lines
lib/certgen/certgen.go	59.09%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #234      +/-   ##
==========================================
+ Coverage   32.13%   32.17%   +0.04%     
==========================================
  Files          75       75              
  Lines        9730     9739       +9     
==========================================
+ Hits         3127     3134       +7     
- Misses       5962     5963       +1     
- Partials      641      642       +1     

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