Push Rules aren't always enabled by default

[t3chguy]

As per the spec https://matrix.org/docs/spec/client_server/r0.6.1#put-matrix-client-r0-pushrules-scope-kind-ruleid

When creating push rules, they MUST be enabled by default.

But in Synapse if you add a push rule, disable it, remove it and re-add a push rule with the same ID then it'll be disabled.

I guess the entry in the push_rules_enable table isn't getting cleared out
This will need to be fixed retroactively for already deleted push rules too.
Looks to also be an opportunity to purge a bunch of stale data from that table for rules which no longer exist.

[richvdh]

this is closely related to matrix-org/matrix-spec-proposals#2655: the fact that synapse permits hidden "enabled" state about non-existent pushrules.

[richvdh]

the impact of this is that when somebody creates a new "keyword" to be notified on, it might not work.

[richvdh]

dup #1475