fix: pass params in url for introspect jwt flow

[medhost-jshaver]

Returning the decoded JWT token payload from introspectJwtToken function, and using string token parameter for call to introspect endpoint since it expects x-www-form-urlencoded content-type.

Issue #, if available:

Description of changes:

1. Changed introspectJwtToken method to return the decoded token payload since the introspect endpoint response doesn't necessarily return the JWT.

For example, our introspect endpoint returns a payload with the "scope" key while the jwt uses "scp".

2. change the token parameter type to a string for the actual introspect call. The Object structure did not seem to place nice with x-www-form-urlencoded content-type.

3. Updated test to reflect the introspectJwtToken returning the decodedToken payload and not the introspect response.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[rsmayda]

Code looks good!

@medhost-jshaver please commit an empty commit with a commit message following conventional commits. Something like the below would work:
fix: pass params in url for introspect jwt flow

@carvantes or @Bingjiling to merge this in and release it.