* Use multi-level logging for shared channel and remote cluster service errors
Service-specific log levels (LvlRemoteClusterServiceError, LvlSharedChannelServiceError)
were hidden from the main log by default, requiring explicit configuration to see them.
Switch all call sites to use LogM with multi-level combos so each log line is attributed
to both the standard level (error/warn) and the service-specific level. This surfaces
errors in the main log while preserving the ability to isolate them into dedicated files.
Each instance was reviewed and either kept as error (DB failures, security issues, config
errors, exhausted retries on critical data) or downgraded to warn (transient network
failures, remote-side reported errors with retry logic, non-critical data like profile
images, reactions, acknowledgements, and status).
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
```
https://mattermost.atlassian.net/browse/MM-52079
```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```
Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
