Handle remote key from kas grants on encrypt

[elizabethhealy]

Right now, when getting kas grants from attributes/values, we only extract the cached keys. However kas grants can have remote keys instead of cached. We currently do not support this.

platform/sdk/granter.go

Line 265 in 32c09c3

keys := kas.GetPublicKey().GetCached().GetKeys()

^ only gets cached
There should be addition steps here to check for other key types like remote, and retrieve them if necessary.

[elizabethhealy]

opentdf/java-sdk#153 (comment)

[cassandrabailey293]

will be discussing further in this sprint, still need to firm up acceptance criteria and our key management and brokering cases. will defer this implementation until after those decisions are made.

[jrschumacher]

@elizabethhealy going to close as not planned right now. If we see that support is needed for remote keys we'll reopen.