Add Altair fork schedule for Pyrmont (#2501)

## Issue Addressed

NA

## Proposed Changes

Adds the Altair fork schedule for Pyrmont, as per eth-clients/eth2-networks#56 (credits to @ajsutton).

## Additional Info

- I've marked this as `do-not-merge` until the upstream PR is merged.
- I've tagged this for `v1.5.0` because I expect the upstream PR to be merged soon, and I think it would be great if v1.5.0 shipped fully ready for the Pyrmont fork.

Author: paulhauner

common/eth2_network_config/built_in_network_configs/pyrmont/config.yaml

@@ -14,20 +14,21 @@ GENESIS_FORK_VERSION: 0x00002009
 # Customized for Pyrmont: 432000 seconds (5 days)
 GENESIS_DELAY: 432000
 
+
 # Forking
 # ---------------------------------------------------------------
 # Some forks are disabled for now:
 #  - These may be re-assigned to another fork-version later
 #  - Temporarily set to max uint64 value: 2**64 - 1
 
 # Altair
-ALTAIR_FORK_VERSION: 0x01000000
-ALTAIR_FORK_EPOCH: 18446744073709551615
+ALTAIR_FORK_VERSION: 0x01002009
+ALTAIR_FORK_EPOCH: 61650
 # Merge
-MERGE_FORK_VERSION: 0x02000000
+MERGE_FORK_VERSION: 0x02002009
 MERGE_FORK_EPOCH: 18446744073709551615
 # Sharding
-SHARDING_FORK_VERSION: 0x03000000
+SHARDING_FORK_VERSION: 0x03002009
 SHARDING_FORK_EPOCH: 18446744073709551615
 
 # TBD, 2**32 is a placeholder. Merge transition approach is in active R&D.
@@ -61,6 +62,7 @@ MIN_PER_EPOCH_CHURN_LIMIT: 4
 # 2**16 (= 65,536)
 CHURN_LIMIT_QUOTIENT: 65536
 
+
 # Deposit contract
 # ---------------------------------------------------------------
 # Ethereum Goerli testnet