continuous-integration/drone/push Build is passingDetails
#### 📖 Summary
- Fix Set-CredentialStoreItem. Currently it doesn't warn if the user is trying to update a CredentialStoreItem, that does not exist.
- Also add a bit of documentation and UnitTests.
- Fix the quotation of Test-CredentialStoreItem.
#### 📑 Test Plan
> 💡 Select your test plan for the code changes.
- [x] Tested via Drone.io pipeline
- [ ] Custom test
- [ ] No test plan
##### Details / Justification
<!-- Add your test details or justification for missing tests here. -->
#### 📚 Additional Notes
<!-- A place for additional detail notes. -->
Co-authored-by: OCram85 <ocram85@noreply.local>
Reviewed-on: #76
Reviewed-by: OCram85 <ocram85@noreply.local>
Co-authored-by: pinguinfuss <christian@heimdaheim.de>
Co-committed-by: pinguinfuss <christian@heimdaheim.de>
