Feat: allow user to define custom template for share name

[dorianim]

Description

This allows users to define a custom letter template in /etc/linuxmuster-linuxclient7/config.yml. e.g.:

shares:
  letterTemplate: "_{letter}"

The default nameTemplate is ({letter}:).

Fixes #33

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Unit tests
• Debian 13 client

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.93%. Comparing base (4939eb7) to head (7b17b43).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
...on3/dist-packages/linuxmusterLinuxclient7/setup.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage   61.47%   61.93%   +0.45%     
==========================================
  Files          18       18              
  Lines        1529     1542      +13     
==========================================
+ Hits          940      955      +15     
+ Misses        589      587       -2     

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