* MM 10658 Change config fields to pointers (#8898)
* Change fields of config structs to pointers and set defaults
MM-10658 https://github.com/mattermost/mattermost-server/issues/8841
* Fix tests that go broken during switching config structs to pointers
MM-10658 https://github.com/mattermost/mattermost-server/issues/8841
* Apply changes of current master while switching config structs to pointers
MM-10658 https://github.com/mattermost/mattermost-server/issues/8841
* Fix new config pointer uses
* Fix app tests
* Fix mail test
* remove debugging statement
* fix TestUpdateConfig
* assign config consistently
* initialize AmazonS3Region in TestS3TestConnection
* initialize fields for TestEmailTest
* fix TestCheckMandatoryS3Fields
* MM-10417 Add local image proxy and enable by default
* Remove unused function
* Add dependencies for willnorris/imageproxy
* Fixed compilation errors
* Lock to the master version of willnorris/imageproxy
* Fix atmos/camo proxy when no SiteURL is specified
* Re-add default values for deprecated settings
* Fix unit tests added by merge
* Pass imageproxy to App struct
* Remove unneeded locking when creating the image proxy
* Remove empty test file
* migrate to idiomatic handling the ReadFile method of LocalFileBackend
* migrate to idiomatic handling the ListDirectory method of LocalFileBackend
* gofmt done
* migrate to idiomatic handling the FileExists method of LocalFileBackend
* api4: improved error handling
* system_store: more logs
* integrate go-junit-report into test-te/test-ee
* add CI_MINIO_HOST and CI_INBUCKET_HOST instead of CI_HOST
* comment re: minio configuration issue
* fix TestStartServerPortUnavailable to pass even when root can bind to :21
* skip TestFindManifest_FolderPermission while running as root
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)
