Fix "default" and overwritten / reset users will not have pubsub channels permissions by default. (#8723)

Background:
Redis 6.2 added ACL control for pubsub channels (#7993), which were supposed
to be permissive by default to retain compatibility with redis 6.0 ACL. 
But due to a bug, only newly created users got this `acl-pubsub-default` applied,
while overwritten (updated) users got reset to `resetchannels` (denied).

Since the "default" user exists before loading the config file,
any ACL change to it, results in an update / overwrite.

So when a "default" user is loaded from config file or include ACL
file with no channels related rules, the user will not have any
permissions to any channels. But other users will have default
permissions to any channels.

When upgraded from 6.0 with config rewrite, this will lead to
"default" user channels permissions lost.
When users are loaded from include file, then call "acl load", users
will also lost channels permissions.

Similarly, the `reset` ACL rule, would have reset the user to be denied
access to any channels, ignoring `acl-pubsub-default` and breaking
compatibility with redis 6.0.

The implication of this fix is that it regains compatibility with redis 6.0,
but breaks compatibility with redis 6.2.0 and 2.0.1. e.g. after the upgrade,
the default user will regain access to pubsub channels.

Other changes:
Additionally this commit rename server.acl_pubusub_default to
server.acl_pubsub_default and fix typo in acl tests.