build: add gci linter

What does this MR do?

Closes #671 (closed)

Related to !534 (closed)

Blocked by !661 (merged)

Note: I suspect the current golangci config is suppressing more issues than it should but that's fixed in the related MR

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines