Rename default Browser Performance Testing job name (breaking change)

This is a follow up from !34634 (merged).

The default job name for Browser Performance Testing is currently named just performance in it's template. After several attempts in the MR to change it to the intended browser_performance it was concluded to not be feasible currently to do this as well as maintain backwards compatibility with users who are using the performance job currently.

In addition to this we should also update the PERFORMANCE_DISABLED AutoDevOps environment variable to BROWSER_PERFORMANCE_DISABLED.

As such, we'll look to do this later as a breaking change making sure to notify users with enough time.