Return HTTP OK Response after user logic execution

[LakshanSS]

Purpose

• Fix https://github.com/wso2-enterprise/choreo/issues/6342

Currently in the listener implementation, the moment we receive the event, we respond with status 200 OK, and then we dispatch the event. At user function implementation if there was an error we throw it up. In this case, as we have already responded with 200 OK, http client cannot convert the error and respond again, because it cannot respond to the same message twice.
Ideally we should respond with status 200 OK only after dispatching the event. At user function implementation if there was an error we throw it up & the http client will return status 500 error. If there is no any errors & the user logic is executed successfully, we should respond with status 200 OK.

Goals

• Return HTTP OK Response after user logic execution

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? no
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes

Related PRs

#45

Test environment

JDK 11
Ballerina SLBeta2