feat: add support for known first party modules

[mkniewallner]

Resolves #247.

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Add the ability to explicitly specify first party modules through known-first-party CLI option (known_first_party in pyproject.toml).

[codecov-commenter]

Codecov Report

Merging #257 (3dc7137) into main (1f0b0cf) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #257   +/-   ##
=====================================
  Coverage   95.7%   95.7%           
=====================================
  Files         32      32           
  Lines        919     922    +3     
  Branches     192     193    +1     
=====================================
+ Hits         880     883    +3     
  Misses        26      26           
  Partials      13      13           

Impacted Files	Coverage Δ
deptry/cli.py	93.6% <100.0%> (+0.1%)	⬆️
deptry/core.py	97.7% <100.0%> (+<0.1%)	⬆️

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