fix!: enforce regex for agent names (#16641)

Underscores and double hyphens are now blocked. The regex is almost the
exact same as the `coder_app` `slug` regex, but uppercase characters are
still permitted.

coderd/workspaceagents_test.go

@@ -393,7 +393,8 @@ func TestWorkspaceAgentConnectRPC(t *testing.T) {
 							Name: "example",
 							Type: "aws_instance",
 							Agents: []*proto.Agent{{
-								Id: uuid.NewString(),
+								Id:   uuid.NewString(),
+								Name: "dev",
 								Auth: &proto.Agent_Token{
 									Token: uuid.NewString(),
 								},