Connect on-page dialog CTA to MoEngage

Background / User story

We need to connect the on-page dialog that we're implementing in #1393 (closed) to MoEngage, which we're integrating in #1368 (closed), so that we can use it from and see its effects in MoEngage.

What to change

• Spec: N/A
• Development: Add support for registering and executing handlers for any incoming "create_on_page_dialog" MoEngage commands.

Hints for testers

This issue doesn't include any command handlers yet (see #1393 (closed)), nor does it include the communication between the extension and MoEngage (see #1368 (closed)). Therefore nothing is expected to happen yet as part of this issue, other than checking that there aren't any obvious problems when building or running the extension.

That being said, we should verify that the Premium license activation/deactivation still works as expected.

Hints for translators

N/A