Add get draft deposition ID method

[znicholls]

Description

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

[codecov]

Codecov Report

Attention: Patch coverage is 88.61789% with 14 lines in your changes missing coverage. Please review.

Project coverage is 82.56%. Comparing base (8d37f51) to head (52af018).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/openscm_zenodo/zenodo.py	88.42%	8 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
+ Coverage   81.10%   82.56%   +1.46%     
==========================================
  Files           5        5              
  Lines         307      327      +20     
  Branches       53       56       +3     
==========================================
+ Hits          249      270      +21     
+ Misses         40       36       -4     
- Partials       18       21       +3     

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