Allow filtering realm keys by use

[justjanne]

Keycloak exposes several fields on realm keys:

{
	"1": {
		"providerId": "...",
		"providerPriority": 100,
		"kid": "...",
		"status": "ACTIVE",
		"type": "RSA",
		"algorithm": "RS256",
		"publicKey": "...",
		"certificate": "...",
		"use": "ENC"
	}
}

Currently the provider allows filtering by type and algorithm. It’d be awesome if it’d also be possible to filter by use.

It looks like it’d just be a change here and here, but I’m unsure whether that’s all that’s needed