v1.5.0 rc.0 (#2506)

## Issue Addressed

NA

## Proposed Changes

- Bump to `v1.5.0-rc.0`.
- Increase attestation reprocessing queue size (I saw this filling up on Prater).
- Reduce error log for full attn reprocessing queue to warn.

## TODO

- [x] Manual testing
- [x] Resolve https://github.com/sigp/lighthouse/pull/2493
- [x] Include https://github.com/sigp/lighthouse/pull/2501

Cargo.lock

@@ -545,7 +545,7 @@ dependencies = [
 
 [[package]]
 name = "beacon_node"
-version = "1.4.0"
+version = "1.5.0-rc.0"
 dependencies = [
  "beacon_chain",
  "clap",
@@ -719,7 +719,7 @@ dependencies = [
 
 [[package]]
 name = "boot_node"
-version = "1.4.0"
+version = "1.5.0-rc.0"
 dependencies = [
  "beacon_node",
  "clap",
@@ -3218,7 +3218,7 @@ dependencies = [
 
 [[package]]
 name = "lcli"
-version = "1.4.0"
+version = "1.5.0-rc.0"
 dependencies = [
  "account_utils",
  "bls",
@@ -3862,7 +3862,7 @@ dependencies = [
 
 [[package]]
 name = "lighthouse"
-version = "1.4.0"
+version = "1.5.0-rc.0"
 dependencies = [
  "account_manager",
  "account_utils",