Doc Feedback: Improve description of Third Party API Feature

[viggnah]

Location:
https://apim.docs.wso2.com/en/4.1.0/deploy-and-publish/publish-on-dev-portal/third-party-api-support/
https://apim.docs.wso2.com/en/4.2.0/deploy-and-publish/publish-on-dev-portal/third-party-api-support/

Would be ideal to update the third party API feature with what can and cannot be expected from it. These points are derived from a discussion on the following internal ticket, so that we can recommend the feature to a customer. Suggestions for improvement -

• Adding the permitted (docs, subscribing etc.) and unpermitted (lifecycle, policies etc.) operations for third party APIs
• Elaborate a bit more on the "special setup" for generating tokens like you already explained
• Add the below screenshot about how details are displayed in an appropriate place if possible (again from the same ticket)
  

Suggested Labels:
APIM 4.1.0, APIM 4.2.0

Affected Product Version:
APIM 4.1.0, APIM 4.2.0

Related Issues:
https://github.com/wso2-enterprise/wso2-apim-internal/issues/5656