Don't rename Prozess_Digitalisierung_PREMIS.xml

[djjuhasz]

Fixes #58

Digitized (Vecteur) SIPs are the only type of SIP that contain a Prozess_Digitalisierung_PREMIS.xml file, and they will only ever contain a single dossier. Because digitized SIPs only have a single dossier that contains a single Prozess_Digitalisierung_PREMIS.xml file there's no need to rename the file in the PIP to avoid name clashes.

Changes:

• Update the SIP identification logic - if a SIP has a Prozess_Digitalisierung_PREMIS.xml file then it must be a digitized SIP
• Add a SIP validation check to confirm that digitized SIPs only contain a single dossier
• Remove the SIP transformation code that renamed the Prozess_Digitalisierung_PREMIS.xml file

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 53.85%. Comparing base (effe3eb) to head (bc5d806). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/activities/transform_sip.go	75.00%	2 Missing and 2 partials :warning:
internal/activities/validate_structure.go	62.50%	2 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #67 +/- ## ========================================== - Coverage 54.06% 53.85% -0.21% ========================================== Files 29 29 Lines 2090 2087 -3 ========================================== - Hits 1130 1124 -6 - Misses 891 893 +2 - Partials 69 70 +1 ```

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