feat: eagerly index all consensus heights (#2163)

Initially we were only indexing consensus heights as they were needed
(to match lightclient_update.revision_height to execution heights). This
leads to a race condition, where briefly the lightclient_update is
joined with the wrong block, as the consensus height is indexed after
the lightclient_update insert.

We now just index all consensus_height-execution_height pairs, such that
the join is always correct.