Send Object to receive task in HTTP payload instead of datastore

[snarfed]

Should cut some of our datastore load, especially if we stop storing transient activities like CRUD altogether.

Re #1149

[snarfed]

Not a huge difference so far, but some reduction in datastore load.

[snarfed]

Reopening, this made us lose our task delay logging for AP and Bluesky receive tasks. When we log, the Object is now new in memory and hasn't been stored yet, so it doesn't have created or updated. Argh.

bridgy-fed/protocol.py

Lines 836 to 839 in 7c71feb

	if request.headers.get('X-AppEngine-TaskRetryCount') == '0' and obj.created:
	delay_s = int((util.now().replace(tzinfo=None) - obj.created).total_seconds())
	delay = f'({delay_s} s behind)'
	logger.info(f'Receiving {from_cls.LABEL} {obj.type} {id} {delay} AS1: {json_dumps(pruned, indent=2)}')

[snarfed]

^ also, not caused by that bug, but while I'm in there, I should improve our delay handling for existing Objects. At minimum we should use updated instead of created, but I need to think harder about whether that's actually right.

[snarfed]

I've temporarily disabled the tasks delayed alert policy. Once I fix this ^, reminder to myself to re-enable it.

[snarfed]

Moved monitoring regression (#1354 (comment)) to new issue #1378.