Update Wiremock to v3 and JUnit5

[bitwiseman]

See https://wiremock.org/docs/junit-jupiter/

GithubWireMockRule creates and manages multiple WireMockServers. Need to do the same for JUnit5 but not sure how composable the JUnit5 WireMock extension is. Might need to move to an abstract base test class that instantiates all the servers.

I think v3 is Java 11+ only but if it isn't do that as well.