"Firmware" tab should be optional

[katsel]

Is your feature request related to a problem? Please describe.

Currently, the "Firmware" tab shows up at the top of the page regardless if cnaas-nms supports firmware updates for the current vendor or not.
It seems like firmware updates are currently mostly an Arista thing but do not work for Juniper -- so for us, this tab is not useful right now.
Making the tab optional would be a way to make the frontend more vendor-independent.

Describe the solution you'd like

I'd suggest the tab to be optional and only show up when the CNAAS_FIRMWARE_URL environment variable is set and non-empty.
If CNAAS_FIRMWARE_URL is set: Show the tab.
Otherwise: Tab is not visible.

Describe alternatives you've considered

Ignoring it? ;) Still every new person I tell about the frontend needs to be told "sorry, we currently can't use this!"

Additional context

It's a really small niggle, I admit that. Still I'd like seeing this fixed.

[indy-independence]

If you are using the SSO authentication with permissions you can hide the firmware tab by not assigning the firmware permission to any users