* [chore] Remove years from all license headers
Years or year ranges aren't required in license headers. Many projects
have removed them in recent years and it avoids a bit of yearly toil.
In many cases our copyright claim was also a bit dodgy since we added
the 2021-2023 header to files created after 2021 but you can't claim
copyright into the past that way.
* [chore] Add license header check
This ensures a license header is always added to any new file. This
avoids maintainers/reviewers needing to remember to check for and ask
for it in case a contribution doesn't include it.
* [chore] Add missing license headers
* [chore] Further updates to license header
* Use the more common // indentend comment format
* Remove the hack we had for the linter now that we use the // format
* Add SPDX license identifier
* reference logrus' global logger instead of passing and storing a logger reference everywhere
* always directly use global logrus logger instead of referencing an instance
* test suites should also directly use the global logrus logger
* rename gin logging function to clarify that it's middleware
* correct comments which erroneously referenced removed logger parameter
* setting log level for tests now uses logrus' exported type instead of the string value, to guarantee error isn't possible
