Follow-up fixes for online wal_level change

Hi all,

While reviewing the online wal_level change feature (commit
67c20979ce7), I found an assertion failure during crash recovery.
Also, I noticed that pg_controldata doesn't show the logical decoding
status. Patches attached.

0001 fixes the assertion failure that happens in the following scenario:

1. Run the server with wal_level = 'replica' and create a logical
slot, which writes an XLOG_LOGICAL_DECODING_STATUS_CHANGE record that
activates logical decoding.
2. Drop the slot, and crash the server before the checkpointer
deactivates logical decoding.
3. Restart the server with wal_level = 'minimal'.

Crash recovery replays the status change record and activates logical
decoding, then UpdateLogicalDecodingStatusEndOfRecovery() fails the
assertion (Assert(!IsXLogLogicalInfoEnabled() &&
!IsLogicalDecodingEnabled())) that logical decoding is never active
with wal_level='minimal'.

I think that replaying the status change record itself is correct, as
it reflects the status at the time the record was written. The problem
is that the end-of-recovery code assumed that this cannot happen,
instead of adjusting the status. Therefore, the fix removes the
wal_level='minimal' special case from
UpdateLogicalDecodingStatusEndOfRecovery() so that it recomputes the
status as usual.

0002 adds the logical decoding status stored in the checkpoint record
to the pg_controldata output, which I found useful while investigating
the above issue.

Both patches are intended to be backpatched to v19.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com