Add get_query_payload to gemini

[nkphysics]

Hey yall, I'm still going through the list #2040 and with this PR I've added the get_query_payload kwarg to gemini.

Specifically I has been added to the following:

• query_criteria
• query_region
• query_object
• quary_raw through **kwargs

I also added a section on inspecting the payload to the docs.

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.05%. Comparing base (b50cfc8) to head (e8f8855).
⚠️ Report is 47 commits behind head on main.

Files with missing lines	Patch %	Lines
astroquery/gemini/core.py	81.81%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3568      +/-   ##
==========================================
+ Coverage   72.76%   73.05%   +0.29%     
==========================================
  Files         219      219              
  Lines       20543    20551       +8     
==========================================
+ Hits        14948    15014      +66     
+ Misses       5595     5537      -58     

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