Allow dicom anonymisation from external users

Description

If we want someone to use our anonymisation externally, this allows them to do this without having to have a pixl database setup. Defaults don't change any behaviour.

Also some general code clean up.

Type of change

Please delete options accordingly to the description.

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[x] This change requires a documentation update

Suggested Checklist

[x] I have performed a self-review of my own code.
[x] I have made corresponding changes to the documentation.
[x] My changes generate no new warnings.
[x] I have commented my code, particularly in hard-to-understand areas.
[x] I have passed on my local host device. (see further details at the CONTRIBUTING document)
[x] Make sure your branch is up-to-date with main branch. See CONTRIBUTING for a general example to syncronise your branch with the main branch.
[x] I have requested PR review to UCLH-Foundtry/arc-dev
[ ] I have adddressed and marked as resolved all the review comments in my PR.
[ ] Finally, I have selected squash and merge

Codecov Report

Attention: Patch coverage is 96.22642% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.65%. Comparing base (5f8b307) to head (cba255e). Report is 1 commits behind head on main.

Files	Patch %	Lines
pixl_dcmd/src/pixl_dcmd/main.py	90.90%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #485 +/- ## ========================================== + Coverage 84.47% 84.65% +0.18% ========================================== Files 84 84 Lines 3619 3624 +5 ========================================== + Hits 3057 3068 +11 + Misses 562 556 -6 ```

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SAFEHR-data / PIXL