Forward/Revert blocks to the specified height

[shunsukew]

Resolve #69

• forward_blocks_to: Forward blocks to the specified block height.
• revert_blocks_to: Revert blocks to the specified block height. (Reverting finalized blocks only works when --state-pruning mode is archive)

Examples

curl http://localhost:9933 -H "Content-Type:application/json;charset=utf-8" -d   '{                                                                                  feat/forward-revert-blocks ✭
     "jsonrpc":"2.0",
      "id":1,
      "method":"engine_forwardBlocksTo",
      "params": [120, null]
    }'
{"jsonrpc":"2.0","result":null,"id":1}%

curl http://localhost:9933 -H "Content-Type:application/json;charset=utf-8" -d   '{                                                                                  feat/forward-revert-blocks ✭
     "jsonrpc":"2.0",
      "id":1,
      "method":"engine_revertBlocksTo",
      "params": [50, null]
    }'
{"jsonrpc":"2.0","result":null,"id":1}% 

[shunsukew]

Backend revert method doesn't work when blocks are finalized for some reason, even though it is described that providing true as the second argument can revert finalized blocks (in unsafe way).

[shunsukew]

paritytech/substrate#14194

[PierreOssun]

LGTM