* [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
* update Activity
* add instance-deliver-to-shared-inboxes setting
* update activity version again
* add SharedInboxURI field to accounts
* serdes for endpoints/sharedInbox
* deliver to sharedInbox if one is available
* update tests
* only assign shared inbox if shared domain
* look for shared inbox if currently nil
* go fmt
* finger to get params.RemoteAccountID if necessary
* make comments clearer
* compare dns more consistently
