Add setting for SSH client configuration file

[isc-pbarton]

Resolves #293

A testing plan:
Clone a GitHub repository via SSH with a private key file. Settings page should say "connection successful" under the Remote Repository input.
Create a new config file with contents matching those suggested here: https://docs.github.com/en/authentication/troubleshooting-ssh/using-ssh-over-the-https-port#enabling-ssh-connections-over-https
Set the "Path to SSH Config File" in settings to that file path and save. It should still say "connection successful".
Set the path to a nonexistent file. It should show an error message under the Remote Repository input.
Clear the value. It should say "connection successful" again.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.30%. Comparing base (749c582) to head (950b04a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cls/SourceControl/Git/Utils.cls	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #877      +/-   ##
==========================================
+ Coverage   49.72%   50.30%   +0.57%     
==========================================
  Files          24       24              
  Lines        3298     3634     +336     
==========================================
+ Hits         1640     1828     +188     
- Misses       1658     1806     +148     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.