Time-bounded measurement of "historical value shielded"

[cwgoes]

It would be useful to be able to capture "users shielding and unshielding some (relatively short) time later" usage in our metrics, as this is a common flow which is not captured by "total value shielded" growth (as the net change is ~0).

We could start with "historical value shielded", but broken out over time, so you could see on the metrics page:

• Value shielded each day (as a graph)
• % change daily/weekly/monthly/etc. in "historical value shielded"

That would already be a solid start, I think, and we could add more later.

[sug0]

I think this endpoint already has this info

namada-indexer/swagger.yml

Lines 611 to 620 in 411639e

	/api/v1/masp/aggregates:
	get:
	summary: Get inflows and outflows from/to the MASP pool
	responses:
	"200":
	description: Get the inflows and outflows from/to the MASP pool
	content:
	application/json:
	schema:
	$ref: "#/components/schemas/MaspPoolAggregateResponse"