adds --arch-dir argument to point to specific architecture directories

[pardallio]

Description

In response to Issue #36

ecbundle build looks for archs either in the arch folder or in the running directory, so the simplest way to do it is just to pass --arch relative/path/from/working/directory/to/extra-archs/(...) but it seems highly non-ideal.

This PR allows an --arch-dir argument to be passed to ecbundle create, which populates the source directory with the folder given in arch-dir.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 40.68%. Comparing base (ce56b30) to head (2c6a5a4).

Files with missing lines	Patch %	Lines
ecbundle/create.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #43      +/-   ##
===========================================
+ Coverage    40.66%   40.68%   +0.01%     
===========================================
  Files           49       49              
  Lines        10156    10161       +5     
===========================================
+ Hits          4130     4134       +4     
- Misses        6026     6027       +1     

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