[no-merge] chore: Document webchat customizations for Twilio [CHI-3574]

[gpaoloni]

Description

Go to https://github.com/techmatters/flex-plugins/blob/50cf11449fe5b30192faa3ce6cce5bf4f550f43c/webchat/CUSTOMIZATIONS.md to see the list of customizations. If you think I'm missing something or that something should be better explained, I would appreciate the feedback!

Checklist

• Corresponding issue has been opened
• New tests added
• Feature flags added
• Strings are localized
• Tested for chat contacts
• Tested for call contacts

Other Related Issues

None

Verification steps

AFTER YOU MERGE

1. Cut a release tag using the Github workflow. Wait for it to complete and notify in the #aselo-deploys Slack channel.
2. Comment on the ticket with the release tag version AND any additional instructions required to configure an environment to test the changes.
3. Only then move the ticket into the QA column in JIRA

You are responsible for ensuring the above steps are completed. If you move a ticket into QA without advising what version to test, the QA team will assume the latest tag has the changes. If it does not, the following confusion is on you! :-P

[stephenhand]

Looks good to me, we might need to do a gap analysis of what our forms engine provides vs what webchat 3 provides, but that seems to be out of scope for this task