CHI-3855: Capture data attributes from the current script so they can be used in event handlers

[stephenhand]

Description

Aselo Webchat runs code from window event handlers rather than directly from the script, which means document.currentScript is null, because it's fired on an event, not a script

This PR captures the data attributes on the script tag ahead of time so they can still be used to override configurations in code running in event handlers

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