Fix hardcoded aud ID value for participant registry

Proposed changes

There is a bug with the JWT aud parameter when requesting an access token at the participant registry/satellite. This was hardcoded with the ID of the iSHARE test instance. This fix changes this parameter to the one from the Keyrock configuration.

Types of changes

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[x] Bugfix (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 not work as expected)

Checklist

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[x] I have read the CONTRIBUTING doc
[x] I have signed the CLA
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] I have added necessary documentation (if appropriate)
[ ] Any dependent changes have been merged and published in downstream modules

ging / fiware-idm