app/obolapi: add exit endpoints

[gsora]

Add partial exit endpoints handlers to Charon's Obol API client package.

Added unit tests and a mock server.

This code was taken and adapted from lido-dv-exit: once this PR gets merged, we'll remove it from there.

category: feature
ticket: #2848

[codecov]

Codecov Report

Attention: Patch coverage is 57.28477% with 129 lines in your changes are missing coverage. Please review.

Project coverage is 53.65%. Comparing base (314d11f) to head (833b29d).

❗ Current head 833b29d differs from pull request most recent head d4ebc8d. Consider uploading reports for the commit d4ebc8d to get more accurate results

Files	Patch %	Lines
app/obolapi/exit.go	57.79%	44 Missing and 21 partials ⚠️
app/obolapi/exit_model.go	56.75%	44 Missing and 20 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2926      +/-   ##
==========================================
- Coverage   53.65%   53.65%   -0.01%     
==========================================
  Files         200      202       +2     
  Lines       28229    28531     +302     
==========================================
+ Hits        15146    15307     +161     
- Misses      11214    11311      +97     
- Partials     1869     1913      +44     

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[sonarcloud]

Quality Gate passed

Issues
10 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
14.3% Duplication on New Code

See analysis details on SonarCloud