[CP-9960] appcheck improvements

[bferenc]

Description

Prevent firebase initialization in unsupported browsers.

Changes

• adds a new "reverse" challenge
• increases token fetch timeout to match the token's expiry
• introduces timeouts for registration and verification
• ignores push service registration errors
• adds a browser type check to FirebaseService

Testing

The extension should still generate appcheck tokens for Chrome and Brave, but not for other browsers.

Screenshots:

Reverse challenge duration

Chrome

Brave

Edge

Checklist for the author

Tick each of them when done or if not applicable.

• I've covered new/modified business logic with Jest test cases.
• I've tested the changes myself before sending it to code review and QA.

[csabbee]

[meeh0w]

Worked nicely in Chrome, but I didn't see the requests in Brave. I probably need to toggle that settings you guys mentioned, but I forgot what it was 😬 If you LMK, I can run that test again.

Tested in Brave as well, works nicely :)