Campfire and Emails on Push to define their own test methods

This issue is part of the epic &9485. See that epic for more context.

About

In #385662 we will only enable the Test button for an integration if the integration model has defined a test.

The Campfire and Emails on Push integrations are the only two models that rely on the default test defined in Integration#test that the test is meaningful and working #213123 (comment 1206699507).

Proposal

Implement a #test method in Integrations::Campfire and Integrations::EmailsOnPush, this can be based largely on Integration#test as it works, but should also be improved if there is an opportunity to.

Also, see #356680 (closed) and #356961 (closed) which need to be addressed and fixed as part of this change too. The developer who picks up this issue should assign themselves to those two issues and close them with this issue. See !106897 (merged) for how #test methods should work, which will give clues about how to fix those other issues.