round 1 of follow-up for metadata (#2277)

* refactoring
* send an empty batch if necessary, as per spec
* don't broadcast no-op updates
* don't trim spaces before validating the key
* bump irctest to cover metadata
* replay existing metadata to reattaching always-on clients
* use canonicalized name everywhere
* use utils.SafeErrorParam in FAIL lines
* validate key names for sub
* fix error for METADATA CLEAR
* max-keys is enforced for channels as well
* remove unlimited configurations
* maintain the limit exactly without off-by-one cases
* add final channel registration check

default.yaml

@@ -724,6 +724,7 @@ oper-classes:
             - "history"      # modify or delete history messages
             - "defcon"       # use the DEFCON command (restrict server capabilities)
             - "massmessage"  # message all users on the server
+            - "metadata"     # modify arbitrary metadata on channels and users
 
 # ircd operators
 opers:
@@ -1087,15 +1088,14 @@ history:
 # e.g., ERGO__SERVER__MAX_SENDQ=128k. see the manual for more details.
 allow-environment-overrides: true
 
-# experimental IRC metadata support for setting key/value data on channels and nicknames.
+# metadata support for setting key/value data on channels and nicknames.
 metadata:
     # can clients store metadata?
     enabled: true
-    # how many keys can a client subscribe to? 
-    # set to 0 to disable subscriptions or -1 to allow unlimited subscriptions.
+    # how many keys can a client subscribe to?
     max-subs: 100
-    # how many keys can a user store about themselves? set to -1 to allow unlimited keys.
-    max-keys: 1000
+    # how many keys can be stored per entity?
+    max-keys: 100
 
 # experimental support for mobile push notifications
 # see the manual for potential security, privacy, and performance implications.