feat: add `/extended/v2/mempool/fees` endpoint (#1795) #1903

Job	Run time
lint	58s
lint-docs	49s
test	3m 34s
test-event-replay	1m 28s
test-btc-faucet	1m 13s
test-rpc	1m 16s
test-2_4 (block-zero-handling)	1m 16s
test-2_4 (faucet-stx)	1m 17s
test-bns	1m 52s
test-bns-e2e	1m 49s
test-2_4 (pox-3-btc-address-formats)	2m 8s
test-rosetta	1m 49s
test-2_4 (pox-3-delegate-aggregation)	1m 39s
test-2_4 (pox-3-delegate-stacking)	1m 41s
test-2_4 (pox-3-delegate-revoked-stacking)	1m 49s
test-subnets	2m 24s
test-2_4 (pox-3-stack-extend-increase)	1m 22s
test-2_4 (pox-3-rosetta-btc-addr-types)	4m 22s
test-2_4 (pox-3-rosetta-cycle-phases)	5m 21s
test-2_4 (pox-3-rosetta-segwit)	2m 1s
test-2_4 (pox-3-burnchain-stack-stx)	1m 38s
test-2_4 (pox-3-burnchain-delegate-stx)	1m 44s
test-rosetta-cli-construction	2m 21s
test-rosetta-cli-data	1m 56s
test-rosetta-construction	1m 52s
build-publish	10m 8s
	59m 47s

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