Implement /epoch/{number}/stakes/

[sandtreader]

We need to move the /spdd endpoint into BlockFrost - and it's a key one for use in Partner Chains. From Epic:

/spdd
(Rename to /epochs/{epoch_number}/stakes)
Note: Current /spdd groups by pool while Blockfrost’s endpoint returns a separate entry for each stake address with the pool as a field. Blockfrost has a separate endpoint /epochs/{epoch_number}/stakes/{pool_id} to get the distribution for a single pool.
Requires storing historical spdd by default

I propose a new SPDDHistory module to store this, capturing output from AccountsState, rather than (over-)extending AccountsState itself.

[sandtreader]

Consider splitting out epoch history from EpochActivityCounter into a new EpochState

[golddydev]

Should I work on this issue before I continue working on /pools/{pool_id}/blocks ?

I am trying to save blocks to epoch_activity_counter, so I should split epoch state first?

[sandtreader]

Doesn't make sense to split this because it can be asked for current epoch blocks etc. Just rename EpochActivityCounter as EpochState and expand it.

[golddydev]

We have spdd_state already. (https://github.com/input-output-hk/acropolis/tree/main/modules/spdd_state)