feat[ibmsm]: Add support for service_credentials secret type

[jgawor]

Description

Add support for service_credentials secret type.

Checklist

Please make sure that your PR fulfills the following requirements:

• Reviewed the guidelines for contributing to this repository
• The commit message follows the Conventional Commits Guidelines.
• Tests for the changes have been updated
• Are you adding dependencies? If so, please run go mod tidy -compat=1.21 to ensure only the minimum is pulled in.
• Docs have been added / updated
• Optional. My organization is added to USERS.md.

Type of Change

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

Other information

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.91%. Comparing base (42a43f0) to head (704ebc5).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #629      +/-   ##
==========================================
+ Coverage   72.16%   73.91%   +1.74%     
==========================================
  Files          26       26              
  Lines        1994     1606     -388     
==========================================
- Hits         1439     1187     -252     
+ Misses        458      314     -144     
- Partials       97      105       +8     

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[jkayani]

LGTM, it's adding support for another secret type and it looks like it works like the others do, so no need to add to docs.

Thanks!