[Device management] Add lab flag for matrix client info account data event

[mnaturel]

Your use case

What would you like to do?

Add a new lab flag for authorizing the sending of matrix client info event for the current device into the account data.

Why would you like to do it?

To be able to enable/disable it at runtime.

How would you like to achieve it?

• Flag should default to false
• Events are only sent when the flag is enabled
• When the flag is turned off, the previously stored account data event for the current device is removed

Have you considered any alternatives?

No response

Additional context

No response

Are you willing to provide a PR?

Yes