Make sure prefix selectors have trailing slashes

Summary:
Wihout the trailing slash, `/tracepoint` matches `/tracepointName` etc.
This is problematic when we need to get all tracepoints etc.

Test Plan: Getting tracepoint status should work on dev deploy

Reviewers: michelle, #engineering

Reviewed By: michelle, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D7357

GitOrigin-RevId: b70c27d8605968ca499ba15d7bc1ecabaad64d10

src/vizier/services/metadata/controllers/tracepoint_store.go

@@ -15,10 +15,10 @@ import (
 )
 
 const (
-	tracepointsPrefix      = "/tracepoint"
-	tracepointStatesPrefix = "/tracepointStates"
-	tracepointTTLsPrefix   = "/tracepointTTL"
-	tracepointNamesPrefix  = "/tracepointName"
+	tracepointsPrefix      = "/tracepoint/"
+	tracepointStatesPrefix = "/tracepointStates/"
+	tracepointTTLsPrefix   = "/tracepointTTL/"
+	tracepointNamesPrefix  = "/tracepointName/"
 )
 
 // TracepointDatastore implements the TracepointStore interface on a given Datastore.