config: backport the rename of fastsync to blocksync (#9259)

This is largely a cherry pick of #6755 with some additional fixups added where detected. 
This change moves the blockchain package to a package called blocksync. Additionally, it renames the relevant uses of the term `fastsync` to `blocksync`.

closes: #9227 

#### PR checklist

- [ ] Tests written/updated, or no tests needed
- [x] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [x] Updated relevant documentation (`docs/`) and code comments, or no
      documentation updates needed

test/e2e/pkg/manifest.go

@@ -88,8 +88,9 @@ type ManifestNode struct {
 	// runner will wait for the network to reach at least this block height.
 	StartAt int64 `toml:"start_at"`
 
-	// FastSync specifies whether to enable the fast sync protocol.
-	FastSync bool `toml:"fast_sync"`
+	// BlockSync specifies the block sync mode: "" (disable), "v0" or "v2".
+	// Defaults to disabled.
+	BlockSync string `toml:"block_sync"`
 
 	// Mempool specifies which version of mempool to use. Either "v0" or "v1"
 	// This defaults to v0.

test/e2e/pkg/testnet.go

@@ -72,7 +72,7 @@ type Node struct {
 	IP               net.IP
 	ProxyPort        uint32
 	StartAt          int64
-	FastSync         bool
+	BlockSync        string
 	StateSync        bool
 	Mempool          string
 	Database         string
@@ -155,7 +155,7 @@ func LoadTestnet(file string) (*Testnet, error) {
 			ABCIProtocol:     Protocol(testnet.ABCIProtocol),
 			PrivvalProtocol:  ProtocolFile,
 			StartAt:          nodeManifest.StartAt,
-			FastSync:         nodeManifest.FastSync,
+			BlockSync:        nodeManifest.BlockSync,
 			Mempool:          nodeManifest.Mempool,
 			StateSync:        nodeManifest.StateSync,
 			PersistInterval:  1,
@@ -297,6 +297,11 @@ func (n Node) Validate(testnet Testnet) error {
 			}
 		}
 	}
+	switch n.BlockSync {
+	case "", "v0":
+	default:
+		return fmt.Errorf("invalid block sync setting %q", n.BlockSync)
+	}
 	switch n.Mempool {
 	case "", "v0", "v1":
 	default: