TP: When adding a capability to a server or delivery service, filter out the capabilities it already has from list

[rawlinp]

I'm submitting a ...

• improvement request (usability, performance, tech debt, etc.)

Traffic Control components affected ...

• Traffic Portal

Current behavior:

When adding a server capability to a server or adding a required capability to a delivery service, the dropdown list includes capabilities that have already been added to the server/delivery service.

New behavior:

The dropdown list should filter out capabilities that have already been added to the server/delivery service.

Minimal reproduction of the problem with instructions:

In Traffic Portal, go to a delivery service > More > Manage required server capabilities > + > Select... and observe that the dropdown list will contain capabilities that the delivery service already has. Note: this same process can be followed for servers, except it's "Manage Capabilities" instead of "Manager required server capabilities".

[Siva-Karthi]

@rawlinp I like to try this. Will do the setup, reproduce and add here if any more info needed