Add vault_ssh modules

[lkubb]

What does this PR do?

Adds execution, state and wrapper modules for the SSH secret backend.

What issues does this PR fix or reference?

Fixes: #58

Merge requirements satisfied?

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 11.63793% with 205 lines in your changes missing coverage. Please review.

Project coverage is 88.93%. Comparing base (e5a0de8) to head (4954b14).
Report is 4 commits behind head on main.

Files	Patch %	Lines
src/saltext/vault/modules/vault_ssh.py	11.63%	205 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
- Coverage   90.53%   88.93%   -1.60%     
==========================================
  Files          66       67       +1     
  Lines       11092    11325     +233     
  Branches     1406     1221     -185     
==========================================
+ Hits        10042    10072      +30     
- Misses        830     1032     +202     
- Partials      220      221       +1     

Flag	Coverage Δ
Linux	88.93% <11.63%> (-1.60%)	⬇️
project	77.67% <11.63%> (-3.98%)	⬇️
py310	?
py39	88.93% <11.63%> (?)
salt_3006_8	88.93% <11.63%> (-1.58%)	⬇️
salt_3007_1	?
tests	95.34% <ø> (+0.04%)	⬆️

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