Fetch `interface type` from `ietf` interface yang model

[frederic-loui]

Fetch interface type from ietf interface yang model

For now when we configure holo via holo-cli, interface type is mandatory and entered in a free form.
However, type seems to be a value from ietf-interfaces or ietf-if-extensions yang model

It would be ideal to be able to select interface type from a discrete list built from ietf-interfaces or ietf-if-extensions or other yang model

This will enforce interface configuration consistency

[rwestphal]

Absolutely. It'd be awesome if we could use the TAB key to choose from different interface types.

This could be extended to all YANG leaves whose type is identityref (e.g. control-plane protocol types).

As a first step, we should investigate if libyang supports iterating over all identities of a specified type. Once confirmed, we can use this capability to generate auto-completion suggestions.

I'll transfer this issue to the holo-cli repo.