GOATS-826 GOATS-828: Add GOA backend to fetch observations around target.

[davner]

• Add tests.

Checklist

• Added a release note in doc/changes using the PR number.

[codecov]

Codecov Report

❌ Patch coverage is 98.30508% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.47%. Comparing base (9f9bf7b) to head (3b2df80).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/goats_tom/api_views/target.py	94.28%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #380      +/-   ##
==========================================
+ Coverage   76.09%   76.47%   +0.37%     
==========================================
  Files         230      232       +2     
  Lines        7203     7319     +116     
  Branches      451      454       +3     
==========================================
+ Hits         5481     5597     +116     
  Misses       1638     1638              
  Partials       84       84              

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