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/templateversions_test.go

@@ -829,6 +829,7 @@ func TestTemplateVersionResources(t *testing.T) {
 							Type: "example",
 							Agents: []*proto.Agent{{
 								Id:   "something",
+								Name: "dev",
 								Auth: &proto.Agent_Token{},
 							}},
 						}, {
@@ -875,7 +876,8 @@ func TestTemplateVersionLogs(t *testing.T) {
 						Name: "some",
 						Type: "example",
 						Agents: []*proto.Agent{{
-							Id: "something",
+							Id:   "something",
+							Name: "dev",
 							Auth: &proto.Agent_Token{
 								Token: uuid.NewString(),
 							},