OIDC Discovery Endpoint does not return correct supported authentication methods

[JKAUSHALYA]

Description:
Open ID configurations retrieved through discovery endpoint [1] does not return the correct supported authentication mechanisms. It is hardcoded in the [2].

"token_endpoint_auth_methods_supported": [
        "client_secret_basic",
        "client_secret_post"
    ], 

[1] curl -v -k --user admin:admin https://localhost:9446/oauth2/oidcdiscovery/.well-known/openid-configuration
[2] https://github.com/wso2-extensions/identity-inbound-auth-oauth/blob/master/components/org.wso2.carbon.identity.oauth/src/main/java/org/wso2/carbon/identity/oauth2/util/OAuth2Util.java#L2544

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