fix: ACNA-2523 - change subscribeToServicesWithCredentialType to use existing (OAuth S2S OR JWT), if either does not exist, then create

[shazron]

closes #73

How Has This Been Tested?

• npm test
• manual test
  • aio app init --standalone app my-app (Create a new app)
  • aio app add service (add an action, say User Management API)
  • aio app add service --use-jwt (add an action, say Analytics)
  • check that the project does not have any duplicate enterprise credentials (no JWT) in Developer Console

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #74 (76472d9) into master (aaf8835) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #74   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          543       540    -3     
  Branches        92        90    -2     
=========================================
- Hits           543       540    -3     

Files Changed	Coverage Δ
lib/index.js	100.00% <100.00%> (ø)

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[moritzraho]

lgtm

[MichaelGoberling]

LGTM. Good timing on the change from @mariam21arauj