perf: Cache responses from PragmAPI

[akhercha]

Current Behavior

We ask the same prices from the Pragma API over & over.

Expected Behavior

We should implement a small cache (probably 1min life) so that it goes a lot faster for the checks.

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NOTE: One idea hanging maybe worth exploring:

Have a parallel service responsible of querying all the Pragma API USD prices every X seconds and fill a hashmap ASSET <=> PRICE accessible by the monitoring service, which will only read it and does not care about querying the API.