Add Branding Features

This is a feature proposal for allowing the status page to be changed to be less closely tied to GitLab.com.

The state of branding right now

Currently, the status page has hardcoded values for the header logo and for the "Contact support" links. This would be fine if it was only used by GitLab.com, but:

• We are not currently dogfooding this.
• This is an Ultimate feature.

As it currently stands, these hardcoded values make the status page much harder to use for our customers.

See this ticket (internal only) for an example of customer impact.

What needs to change

The logo and the support links should not be hardcoded.

MVC could probably have something as simple as "if this file exists, change these values." I'd be willing to implement it myself if I could get some guidance on how it should be done.