Previously we intentially did not set settled_at and settle_index when
inserting a new invoice as those fields are set when we settle an
invoice through the usual invoice update. As migration requires that we
set these nullable fields, we can safely add them.
Previously SQL invoice updater ignored the set ID hint when updating an
AMP invoice resulting in update subscriptions returning all of the AMP
state as well as all AMP HTLCs. This commit synchornizes behavior with
the KV implementation such that we now only return relevant AMP state
and HTLCs when updating an AMP invoice.
This commit attempts to fix some issues with the invoice store's schema that we
couldn't foresee before the implementation was finished. This is safe as the
schema has not been instantiated yet outside of unit tests. Furthermore the
commit updates invoice store SQL queries according to fixes in the schema as
well as to prepare the higher level implementation in the upcoming commits.
