There were multiple problems with loading of a license.
1. It was called from inside app/server.go and app/platform/service.go. The first one wasn't really needed anymore, so we remove it.
2. To make loading of a license work across a cluster, the license load action was attached along with the `InvalidateAllCachesSkipSend` method. But the problem with that was that it would even get called in the caller node as well, putting it in a recursive loop.
```
LoadLicense -> SaveLicense -> InvalidateAllCaches -> InvalidateAllCachesSkipSend -> LoadLicense
```
To fix this, we create a dedicated loadLicense cluster event and move it away from the `InvalidateAllCachesSkipSend` method. And then from the caller side, we just trigger this action.
3. We also remove the first call to check license expiration which would load the license again. This is unnecessary because if the license is expired, server wouldn't start at all.
While here, we also make some other improvements like removing unnecessary goroutine spawning while publishing websocket events. They are already handled asynchronously, so there is no need
to create a goroutine for that.
We also remove
```
ps.ReloadConfig()
ps.InvalidateAllCaches()
```
from requestTrialLicense as they are already called from inside `*PlatformService.SaveLicense`.
And lastly, we remove the `*model.AppError` return from `*PlatformService.InvalidateAllCaches` because there was nothing to return at all.
https://mattermost.atlassian.net/browse/MM-53879
```release-note
Fix several issues with loading of a license
```
It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.
https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.
For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```
