* Vendor slack plugin and supporting libraries
* Fix up plugin integration tests (wip)
* Run GCI on vendored code
* Use newtype instead of type alias
golangci-lint currently panics on this,
"skip-files" et al don't help, as it is a linter panic, not an error
See d717045480
* Remove long-runing plugins tests from difftest
* Move access plugin tests to unit-tests-integrations
