* MM-23666: rewrite TestHTTPClient
The existing `TestHTTPClient` actually tries to reach google.com, making it brittle to network hiccups (as unlikely as that might be). Rewrite the test to rely on a local server instead.
I found the existing implementation of `TestHTTPClient` extremely hard to understand, so I've rewritten it more explicitly, expanded coverage somewhat. In doing so, I found myself somewhat surprised by the current behaviour. If `allowHost` returns `true`, we ignore `allowIP` altogether. If `allowHost` returns `false`, we check with `allowIP`. There's a lack of symmetry here that the current filter names don't make clear. Perhaps `allowHost` should be renamed `skipIPCheckForHost`?
Fixes: https://mattermost.atlassian.net/browse/MM-23666
* more compact assertions
* Consistent license message for all the go files
* Fixing the last set of unconsistencies with the license headers
* Addressing PR review comments
* Fixing busy.go and busy_test.go license header
* MM-15276: Migrate Team.Update to sync by default
* MM-15276: Addressing review comments and change Update func signature similar to other interface Update method
* update store mocks for update fn
* addressing review comments
Previously, mattermost-server would always request with the default
user-agent of Go's net/http package that is `Go-http-client/1.1` or
something similar.
This has several disadvantages, one is that the default user-agent
made it pretty hard to distinguish mattermost requests from other
service requests in a network log for example.
Now a user-agent of the form `mattermost-<current-version>` is set in
the client.
- [x] Added or updated unit tests (required for all new features)
