Implement checkpoint sync (#2244)

## Issue Addressed

Closes #1891
Closes #1784

## Proposed Changes

Implement checkpoint sync for Lighthouse, enabling it to start from a weak subjectivity checkpoint.

## Additional Info

- [x] Return unavailable status for out-of-range blocks requested by peers (#2561)
- [x] Implement sync daemon for fetching historical blocks (#2561)
- [x] Verify chain hashes (either in `historical_blocks.rs` or the calling module)
- [x] Consistency check for initial block + state
- [x] Fetch the initial state and block from a beacon node HTTP endpoint
- [x] Don't crash fetching beacon states by slot from the API
- [x] Background service for state reconstruction, triggered by CLI flag or API call.

Considered out of scope for this PR:

- Drop the requirement to provide the `--checkpoint-block` (this would require some pretty heavy refactoring of block verification)


Co-authored-by: Diva M <divma@protonmail.com>

Cargo.lock

@@ -895,6 +895,7 @@ dependencies = [
  "environment",
  "error-chain",
  "eth1",
+ "eth2",
  "eth2_config",
  "eth2_libp2p",
  "eth2_ssz 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -909,6 +910,7 @@ dependencies = [
  "parking_lot",
  "prometheus",
  "reqwest",
+ "sensitive_url",
  "serde",
  "serde_derive",
  "serde_yaml",
@@ -938,17 +940,6 @@ dependencies = [
  "cc",
 ]
 
-[[package]]
-name = "colored"
-version = "1.9.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f4ffc801dacf156c5854b9df4f425a626539c3a6ef7893cc0c5084a23f0b6c59"
-dependencies = [
- "atty",
- "lazy_static",
- "winapi",
-]
-
 [[package]]
 name = "compare_fields"
 version = "0.2.0"
@@ -1714,6 +1705,7 @@ dependencies = [
  "sensitive_url",
  "serde",
  "serde_json",
+ "store",
  "types",
  "zeroize",
 ]
@@ -3065,6 +3057,7 @@ dependencies = [
  "deposit_contract",
  "directory",
  "dirs",
+ "env_logger 0.9.0",
  "environment",
  "eth1_test_rig",
  "eth2_keystore",
@@ -3081,8 +3074,8 @@ dependencies = [
  "regex",
  "sensitive_url",
  "serde",
+ "serde_json",
  "serde_yaml",
- "simple_logger",
  "state_processing",
  "tokio",
  "tree_hash 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -5628,19 +5621,6 @@ dependencies = [
  "rand_core 0.6.3",
 ]
 
-[[package]]
-name = "simple_logger"
-version = "1.13.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b7de33c687404ec3045d4a0d437580455257c0436f858d702f244e7d652f9f07"
-dependencies = [
- "atty",
- "chrono",
- "colored",
- "log",
- "winapi",
-]
-
 [[package]]
 name = "simulator"
 version = "0.2.0"
@@ -6774,6 +6754,7 @@ dependencies = [
  "serde_json",
  "serde_yaml",
  "slog",
+ "state_processing",
  "superstruct",
  "swap_or_not_shuffle",
  "tempfile",