Include IntelliJ run configurations in CONTRIBUTING.md

[picimako]

Since #2273 introduced IntelliJ run configurations for WireMock, as discussed on #2274, they are now mentioned in CONTRIBUTING.md as well for better visibility.

References

#2273, #2274

Submitter checklist

• The PR request is well described and justified, including the body and the references
• The PR title represents the desired changelog entry
• The repository's code style is followed (see the contributing guide)
• Test coverage that demonstrates that the change works as expected
• For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org

[oleg-nenashev]

Thanks!