Limit number of blocks per level (2nd attempt) (#1559)

Prevents the StateDbError::TooManySiblingBlocks error from being triggered by eagerly removing 
stale blocks from the backend on block import and before the error condition is met.

Introduces a just in time block recovery mechanism for blocks that were wrongly removed
via an explicit pov-recovery method

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

client/consensus/common/Cargo.toml

@@ -10,6 +10,7 @@ async-trait = "0.1.59"
 codec = { package = "parity-scale-codec", version = "3.0.0", features = [ "derive" ] }
 dyn-clone = "1.0.10"
 futures = "0.3.25"
+log = "0.4.17"
 tracing = "0.1.37"
 
 # Substrate
@@ -24,7 +25,9 @@ sp-trie = { git = "https://github.com/paritytech/substrate", branch = "master" }
 polkadot-primitives = { git = "https://github.com/paritytech/polkadot", branch = "master" }
 
 # Cumulus
+cumulus-primitives-core = { path = "../../../primitives/core" }
 cumulus-relay-chain-interface = { path = "../../relay-chain-interface" }
+cumulus-client-pov-recovery = { path = "../../pov-recovery" }
 
 [dev-dependencies]
 futures-timer = "3.0.2"