ConfigGetRequest should support exact name instead of only prefix

[briancain]

Describe the bug

Currently our ConfigGetRequest only supports looking up config variables by a prefix. If the prefix matches multiple config vars, it returns them all. There's no way to look up a specific config var only.

waypoint/pkg/server/proto/server.proto

Lines 4671 to 4701 in 596cf48

	message ConfigGetRequest {
	// scope is the scoping for this config variable. This describes the
	// target environment requesting configuration. For runners, this may still
	// be set if you are an on-demand runner requesting variables that may be
	// set for runners only in a specific project/app.
	oneof scope {
	Ref.Application application = 2;
	// For project scope, for historical reason, we return all matching
	// config vars (for all apps). We do not merge by name or perform
	// resolution logic. This is how this has always behaved.
	Ref.Project project = 3;
	}
	// Runner is specified if the requesting environment is a runner environment.
	Ref.RunnerId runner = 4;
	// Workspace that the target environment is in. This will limit configuration
	// values to those that are only for this workspace. If this isn't set, all
	// configuration values will be returned.
	Ref.Workspace workspace = 5;
	// Labels that are set in the target environment. This will limit the
	// configuration values to those which have label selectors that match (or
	// those that just ignore labels).
	map<string, string> labels = 6;
	// Get all configuration entries under the given prefix. When empty,
	// returns all config variables.
	string prefix = 1;
	}

waypoint/pkg/server/proto/server.proto

Lines 4698 to 4700 in 596cf48

	// Get all configuration entries under the given prefix. When empty,
	// returns all config variables.
	string prefix = 1;

This might be surprising behavior if a user knows exactly what they want to look up and they aren't interested in prefix matching for all cases.

Steps to Reproduce

• Create some config vars that start with the same string
• Call waypoint config get my-prefix where my-prefix is the same string prefix that you set
• See them all returned (this is currently by design)

Expected behavior

I imagine it might be nice to for this endpoint to have an exact lookup rather than a prefix.

Waypoint Platform Versions
Additional version and platform information to help triage the issue if
applicable:

• Waypoint CLI Version:
• Waypoint Server Platform and Version: (like docker, nomad, kubernetes)
• Waypoint Plugin: (like aws/ecs, pack, azure)

Additional context
Add any other context about the problem here.