Calling app.DeletePost immediately after creating a post
is susceptible to replica lag because we were calling the
replica to check for the post.
We fix this by passing a context to always query master.
https://mattermost.atlassian.net/browse/MM-58038
```release-note
NONE
```
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
```
