Added support for requirement.txt

[fpgmaas]

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

[codecov-commenter]

Codecov Report

Merging #87 (10baa25) into main (f1cbe09) will increase coverage by 2.1%.
The diff coverage is 96.9%.

@@           Coverage Diff           @@
##            main     #87     +/-   ##
=======================================
+ Coverage   92.6%   94.7%   +2.1%     
=======================================
  Files         24      28      +4     
  Lines        718     973    +255     
=======================================
+ Hits         665     922    +257     
+ Misses        53      51      -2     

Impacted Files	Coverage Δ
deptry/cli_defaults.py	100.0% <ø> (ø)
deptry/dependency.py	97.6% <ø> (ø)
deptry/config.py	96.3% <86.3%> (-3.7%)	⬇️
deptry/dependency_specification_detector.py	88.5% <88.5%> (ø)
deptry/dependency_getter/requirements_txt.py	98.5% <98.5%> (ø)
deptry/dependency_getter/pyproject_toml.py	96.0% <100.0%> (ø)
deptry/import_parser.py	78.7% <100.0%> (ø)
deptry/python_file_finder.py	100.0% <100.0%> (ø)
tests/test_cli.py	100.0% <100.0%> (ø)
tests/test_config.py	100.0% <100.0%> (ø)
... and 5 more

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