Improve ColocatedData.to_dataframe() method

[thorbjoernl]

Change Summary

I found the current implementation of ColocatedData.to_dataframe() lacking so I expanded it a bit.

Produced data frames will now include:

• Time
• Station name
• Data source (obs/mod)
• Latitude
• Longitude
• Altitude
• Variable value (obs/mod)

Related issue number

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 78.87%. Comparing base (f0acbf6) to head (23809dc).
Report is 38 commits behind head on main-dev.

Files with missing lines	Patch %	Lines
pyaerocom/colocation/colocated_data.py	75.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1369      +/-   ##
============================================
+ Coverage     78.85%   78.87%   +0.01%     
============================================
  Files           136      136              
  Lines         20849    20863      +14     
============================================
+ Hits          16441    16455      +14     
  Misses         4408     4408              

Flag	Coverage Δ
unittests	78.87% <75.00%> (+0.01%)	⬆️

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[lewisblake]

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