Add "/easycla" trigger for GitLab

[jarias-lfx]

Summary

Please add "/easycla" action for GitLab

Background

The use of "/easycla" comment in GitHub is a critical feature used by maintainers, contributors and support to trigger EasyCLA bot when required. The use of this feature is very important to have for GitLab as well as we would have no other way to trigger EasyCLA checks in a MR.

[dealako]

1. Need to ensure we are subscribed to receive comment events from GitLab via the webhook
2. Need to add a comment handler routine to review the comments to determine if the current/most-recent comment includes the /easycla command.
3. If the /easycla command is recognized, then the logic should execute the merge request check logic which would re-evaluate the authorized users and ultimately update the GitLab status on the GitLab UI.

[thakurveerendras]

Tested issue on dev site and covered below scenario & found that it is fixed as expected.

Scenario 1 : Comments is disabled on existing setup

Steps & results :

1. Comments is disabled on existing setup
2. Cla is already enforced for existing GitLab group
3. Now disable cla enforced
4. See-Cla hooks configurations disappears at GitLab settings page
5. Re-enabled cla enforced
6. See-Webbooks re-added with comment box is checked as expected,

Scenario 2 : Added fresh GitLab group

Steps & results :

1. Configure(install) new GitLab group
2. See-cla is not added under Webbooks
3. Cla enforced GitLab project
4. See-Webbooks added with comment box is checked as expected,

Scenario 3 : checked /easycla comment behaviour

1. GitLab MR gated with not covered
2. Add /easycla comment
3. See-Note Hook activity logs generated
4. Singed ICLA MR
5. See-MR get covered
6. Add /easycla comment
7. See-Note Hook activity logs generated
   
   

[thakurveerendras]

As confirmed by @jarias-lfx over slack , issue is properly fix & deployed to production too, So moving issue status Done

[shyam-goshike]

Closing as per comments from @jarias-lfx