storage/consensus: Update indexes to better serve the related accounts queries

[ptrus]

Fixes/mitigations for: #882
Fixes: #883

The ix_transactions_method_height was missing the tx_index, so the query optimizer didn't do the top-n optimization for consensus related accounts query with filters on method. The indexes on both tables now match on the fields and ordering, so this should be fixed.

For the https://nexus.oasis.io/v1/consensus/accounts/oasis1qrg3zwe9gvkvs6dvrytr3dedyyjyxp6kgv8u2m2m counting the huge number of related transactions appears to be problematic:

nexus/storage/client/queries/queries.go

Lines 218 to 222 in 0ef5fe5

	AccountStats = `
	SELECT
	COUNT(*)
	FROM chain.accounts_related_transactions
	WHERE account_address = $1::text`

hopefully the increased timeout fixes this. Otherwise we should probably move this computation into the accounts_list view, and fetch it from there.

The last query is using the indexes as expected, it just takes long due the table being huge. Hopefully, the increased timeout helps. In future we should check if there's any db setting optimizations to be done.