I updated the PR and forgot to update the changelog.

This was incorrectly merged to the release branch before it was ready.

This reverts commit 72fe2aff.

Add changelog

Save retrieved keys to the db

lint

Fix and de-brittle remote result dict processing

Use query_user_devices instead, assume only master, self_signing key types

Make changelog more useful

Remove very specific exception handling

Wrap get_verify_key_from_cross_signing_key in a try/except

Note that _get_e2e_cross_signing_verify_key can raise a SynapseError

lint

Add comment explaining why this is useful

Only fetch master and self_signing key types

Fix log statements, docstrings

Remove extraneous items from remote query try/except

lint

Factor key retrieval out into a separate function

Send device updates, modeled after SigningKeyEduUpdater._handle_signing_key_updates

Update method docstring

Fixes: #7127
Signed-off-by: David Vo <david@vovo.id.au>

add a lock to try to make this metric actually work

This should be safe to do on all workers/masters because it is guarded by
a config option which will ensure it is only actually done on the worker
assigned as a pusher.