Deprecate ambiguous svids_count field in Agent GetDebug API

Introduce new SVID count fields for each SVID cache in SPIRE Agent.
These new fields clarify what exactly is represented in the counts and
provide integration tests a way to assert on the state of the various
Agent in-memory caches.

Signed-off-by: Ryan Turner <turner@uber.com>

proto/spire/api/agent/debug/v1/debug.proto

@@ -27,7 +27,14 @@ message GetInfoResponse {
     // Agent uptime in seconds
     int32 uptime = 2;
     // Number of SVIDs cached in memory
-    int32 svids_count = 3;
+    // Deprecated in favor of cached_x509_svids_count, cached_jwt_svids_count, and cached_svidstore_x509_svids_count
+    int32 svids_count = 3 [deprecated=true];
     // last successful sync with server (in seconds since unix epoch)
     int64 last_sync_success = 4;
+    // Number of X.509-SVIDs in Agent primary in-memory cache
+    int32 cached_x509_svids_count = 5;
+    // Number of JWT-SVIDs in Agent primary in-memory cache
+    int32 cached_jwt_svids_count = 6;
+    // Number of X.509-SVIDs in Agent svidstore in-memory cache
+    int32 cached_svidstore_x509_svids_count = 7;
 }