Override the default authenticationUrl value which added in the Implicit Grant type

[piyumaldk]

Fixes https://github.com/wso2/api-manager/issues/2478

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 44.66%. Comparing base (df47529) to head (2915589). Report is 21 commits behind head on master.

Files	Patch %	Lines
...so2/carbon/apimgt/impl/definitions/OAS2Parser.java	50.00%	0 Missing and 2 partials :warning:
...so2/carbon/apimgt/impl/definitions/OAS3Parser.java	83.33%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #12310 +/- ## ============================================ + Coverage 42.22% 44.66% +2.44% - Complexity 0 3655 +3655 ============================================ Files 1840 1840 Lines 136407 136414 +7 Branches 19734 19738 +4 ============================================ + Hits 57598 60933 +3335 + Misses 71882 68185 -3697 - Partials 6927 7296 +369 ``` | [Flag](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12310/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | Coverage Δ | | |---|---|---| | [integration_tests](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12310/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `39.11% <40.00%> (+3.48%)` | :arrow_up: | | [unit_tests](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12310/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `20.45% <70.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[piyumaldk]

Carbon APIMGT tests are passing locally

[piyumaldk]

Product APIM build (tests are skipped) is successful with the changes. Fix is working fine in the pack.