Mattermost-server: Refactor "app/server.go" to use structured logging

[mattermod]

Mattermost is refactoring the logs to be fully structured and we're looking for contributors to help with that effort. This Help Wanted issue is to change the usages of mlog. methods with fmt.Sprintf to proper mlog.Field() calls in file app/server.go.

The expected way to implement it is to open the file app/server.go, look for all calls to mlog.Info, mlog.Debug, etc and in cases where fmt.Sprintf is used to write the log - modify the call to use mlog.Bool, mlog.String, etc to pass the parameters, instead of passing them as part of the format string to Sprintf.

Example: https://github.com/mattermost/mattermost-server/pull/12038

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JIRA: https://mattermost.atlassian.net/browse/MM-18270

[Lumexralph]

@mattermod I would love to work on this.

[hanzei]

Thanks @Lumexralph :+1:

[Lumexralph]

@hanzei A PR is up for this, feedback will be appreciated.