Fix Sub Claim and Introspection Response in Application Tokens

[SujanSanjula96]

Proposed changes in this pull request

• Change the sub claim of the JWT access tokens issued for authenticated applications to client id.
• Remove the username field of the introspection response from the access tokens issued for authenticated applications.

Related Issue - wso2/product-is#14771

When should this PR be merged

Should merge after this PR - wso2/carbon-identity-framework#4633

Follow up actions

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