Any error sent to Sentry will now be marked with the environment they
were sent from. The environment is set at build time, and is set
dependant upon the build flags and CI-related environment variables.
Setting the environment will let us filter error reports in Sentry to
focus specifically upon reports sent from production, release
candidates, PR testing, or whatever else.
Previously, all errors encountered during testing or production were
sent to the primary `metamask` Sentry project, whereas development
errors were sent to `test-metamask` instead. This change ensures that
errors encountered during tests are sent to `test-metamask` as well.
