Switch concurrent replay from feature to param

[bw-solana]

Problem

Concurrent slot replay has been merged (ref: #26465) but is currently not active and controlled by a feature switch. Feature switch is unnecessary in this case, and parameter would allow some set of validators to opt in to testing this capability.

Summary of Changes

Add replay_slots_concurrently parameter to enable replaying of slots from different forks concurrently during replay stage.

[carllin]

Could we also delete concurrent_replay_of_forks from bank.rs and the features from feature_set.rs?

[bw-solana]

Confirmed things are behaving as expected when passing --replay-slots-concurrently (and not):

[2022-08-26T16:42:24.107844950Z WARN  solana_core::replay_stage] BWLOG: 2 active bank(s) to replay: [147596255, 147596280] - replay_slots_concurrently = true
[2022-08-26T16:42:24.209024789Z WARN  solana_core::replay_stage] BWLOG: 2 active bank(s) to replay: [147596255, 147596280] - replay_slots_concurrently = true
[2022-08-26T16:42:24.425800993Z WARN  solana_core::replay_stage] BWLOG: 2 active bank(s) to replay: [147596255, 147596281] - replay_slots_concurrently = true
[2022-08-26T16:42:24.580161181Z WARN  solana_core::replay_stage] BWLOG: 1 active bank(s) to replay: [147596282] - replay_slots_concurrently = true
[2022-08-26T16:42:24.799247359Z WARN  solana_core::replay_stage] BWLOG: 1 active bank(s) to replay: [147596283] - replay_slots_concurrently = true
[2022-08-26T16:42:24.970696365Z WARN  solana_core::replay_stage] BWLOG: 0 active bank(s) to replay: [] - replay_slots_concurrently = true
[2022-08-26T16:42:24.971277319Z WARN  solana_core::replay_stage] BWLOG: 0 active bank(s) to replay: [] - replay_slots_concurrently = true
[2022-08-26T16:42:25.072083812Z WARN  solana_core::replay_stage] BWLOG: 0 active bank(s) to replay: [] - replay_slots_concurrently = true
[2022-08-26T16:42:25.175823842Z WARN  solana_core::replay_stage] BWLOG: 1 active bank(s) to replay: [147596284] - replay_slots_concurrently = true