Return all hotspots which belonged to account at some point

[davetapley]

The v1/accounts/:address/hotspots endpoint only returns hotspots which currently belong to an account.

As noted on davetapley/helium-tax#49, this creates a problem for tax reporting.

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If I'm correct that there's currently no way to get such a list of hotspots from the API,
then could we get a new endpoint (or filter on v1/accounts/:address/hotspots)?

[davetapley]

Relevant links:

blockchain-http/src/bh_route_hotspots.erl

Lines 419 to 433 in 24e5010

	get_hotspot_list([
	{owner, Owner},
	{city, undefined},
	{filter_modes, FilterModes0},
	{cursor, undefined}
	]) ->
	FilterModes =
	case FilterModes0 of
	undefined -> ?HOTSPOT_MODES;
	_ -> FilterModes0
	end,
	Result = ?PREPARED_QUERY(?S_OWNER_HOTSPOT_LIST, [
	Owner,
	FilterModes
	]),

And:

blockchain-http/priv/hotspots.sql

Lines 55 to 56 in 24e5010

	-- :owner_hotspot_list_source
	from (select * from gateway_inventory where owner = $1) as g

[davetapley]

Alas looking at gateway_inventory on https://etl.dewi.org/ it only includes current owners 😞

transactions_transfer_hotspot has it,
but we first need a transactions_transfer_hotspot.sql in /priv/ with something like:

select buyer, seller, gateway from transactions_transfer_hotspot
where seller = $1

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I might have a go at a PR, but I haven't Erlang'd for a long time, so it might not be pretty 😆