[feature] Import Tomes from Private Repos (git ssh)

[KCarretto]

What type of PR is this?

/kind feature

What this PR does / why we need it:

• Adds support for importing tomes from private git repos using SSH public keys
• Configure GIT_SSH_PRIVATE_KEY env variable for tavern, or it will auto-generate a key pair
• Obtain Tavern's public key via a new GraphQL query gitPublicKey
• Import tomes with ssh:// git URL to automatically use this authentication mechanism

[codecov]

Codecov Report

Attention: 123 lines in your changes are missing coverage. Please review.

Comparison is base (f03960d) 73.17% compared to head (57fdbce) 71.01%.

Files	Patch %	Lines
tavern/internal/ent/schema/repository.go	43.33%	50 Missing and 1 partial ⚠️
tavern/tomes/git.go	50.64%	34 Missing and 4 partials ⚠️
tavern/internal/graphql/mutation.resolvers.go	40.62%	15 Missing and 4 partials ⚠️
tavern/internal/graphql/query.resolvers.go	25.00%	7 Missing and 2 partials ⚠️
tavern/internal/ent/schema/tome.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #617      +/-   ##
==========================================
- Coverage   73.17%   71.01%   -2.16%     
==========================================
  Files         115      170      +55     
  Lines        8142    11411    +3269     
==========================================
+ Hits         5958     8104    +2146     
- Misses       2184     3094     +910     
- Partials        0      213     +213     

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