Custom namestring for the Habor instance

[tostt]

Is your feature request related to a problem? Please describe.
When using multiple instances of Harbor it woud be nice to ne able to differentiate them just by looking at the UI.
I am proposing to add a custom namestring to the instance.
I currently use the dark and light themes to differentiate two instances, but this is not ideal.

Describe the solution you'd like
The custom instance namestring would appear under the Harbor title such as show below.

• Left image: the current UI, which would be used if no custom namestring is defined.
• Center and right image: example of the UI in the case of 2 instances with different namestrings.

Describe the main design/architecture of your solution
The (optional) namestring would be defined by an administrator in the instance configuration on the "System Settings" page.