[6.0] Bump swift-syntax in template to 600.0.0-latest (#7445)

Cherry-pick of #7443.

**Explanation**: `swift package init --type macro` template is outdated.
**Scope**: Limited to `swift package init`.
**Risk**: No risks.
**Testing**: Manually verified that `swift package init --type macro`
with freshly built `swift-package` binary creates a package with correct
versions.
**Issues**: 
rdar://124160537
rdar://112626159

**Reviewer**: @ahoppen and @bnbarham

Author: MaxDesiatov

Sources/PackageModel/InstalledSwiftPMConfiguration.swift

@@ -33,6 +33,14 @@ public struct InstalledSwiftPMConfiguration: Codable {
     public let swiftSyntaxVersionForMacroTemplate: Version
 
     public static var `default`: InstalledSwiftPMConfiguration {
-        return .init(version: 0, swiftSyntaxVersionForMacroTemplate: .init(major: 509, minor: 0, patch: 0))
+        return .init(
+            version: 0,
+            swiftSyntaxVersionForMacroTemplate: .init(
+                major: 600,
+                minor: 0,
+                patch: 0,
+                prereleaseIdentifier: "latest"
+            )
+        )
     }
 }

Utilities/config.json

@@ -1 +1 @@
-{"version":1,"swiftSyntaxVersionForMacroTemplate":{"major":510,"minor":0,"patch":0, "prereleaseIdentifier":"latest"}}
+{"version":1,"swiftSyntaxVersionForMacroTemplate":{"major":600,"minor":0,"patch":0, "prereleaseIdentifier":"latest"}}