Plumb context where it's missing, and where possible

[rvagg]

This is just the begining of a rabbit hole dive that I'm going to have to bail on. Building on @virajbhartiya's branch from #12733 attempting to get the right context to where it matters, or add the tag to the context where it doesn't make sense to do it.

Still seeing these (not all of these should be changed btw, a lot of them are CLI contexts and other tooling pieces that don't matter so for the purpose of the original PR):

$ git grep context.Background | grep -v _test | wc
    135     783   11207
$ git grep context.TODO | grep -v _test | wc
    149     997   13530

 curl -s http://localhost:1235/debug/metrics | grep -v '^#' | grep 'network=""' | awk -F\{ '{print $1}' | uniq

Still shows these as missing on this branch:

lotus_block_failure
lotus_block_received
lotus_block_success
lotus_block_validation_ms_bucket
lotus_block_validation_ms_sum
lotus_block_validation_ms_count
lotus_chain_node_height
lotus_chain_node_worker_height
lotus_message_failure
lotus_message_received
lotus_message_success
lotus_message_validation_ms_bucket
lotus_message_validation_ms_sum
lotus_message_validation_ms_count
lotus_message_validation_ms_bucket
lotus_message_validation_ms_sum
lotus_message_validation_ms_count
lotus_mpool_add_ms_bucket
lotus_mpool_add_ms_sum
lotus_mpool_add_ms_count
lotus_mpool_addts_ms_bucket
lotus_mpool_addts_ms_sum
lotus_mpool_addts_ms_count
lotus_mpool_getbalance_ms_bucket
lotus_mpool_getbalance_ms_sum
lotus_mpool_getbalance_ms_count
lotus_mpool_getnonce_ms_bucket
lotus_mpool_getnonce_ms_sum
lotus_mpool_getnonce_ms_count
lotus_mpool_message_count
lotus_peer_count
lotus_pubsub_delivered
lotus_pubsub_duplicate
lotus_pubsub_prune
lotus_pubsub_recv_rpc
lotus_pubsub_rejected
lotus_pubsub_send_rpc
lotus_rcmgr_allow_mem
lotus_vm_applied
lotus_vm_applyblocks_cron_bucket
lotus_vm_applyblocks_cron_sum
lotus_vm_applyblocks_cron_count
lotus_vm_applyblocks_early_bucket
lotus_vm_applyblocks_early_sum
lotus_vm_applyblocks_early_count
lotus_vm_applyblocks_flush_bucket
lotus_vm_applyblocks_flush_sum
lotus_vm_applyblocks_flush_count
lotus_vm_applyblocks_messages_bucket
lotus_vm_applyblocks_messages_sum
lotus_vm_applyblocks_messages_count
lotus_vm_applyblocks_total_ms_bucket
lotus_vm_applyblocks_total_ms_sum
lotus_vm_applyblocks_total_ms_count
lotus_vm_execution_running
lotus_vm_execution_waiting
lotus_vm_sends