Create a --fetch option to allow fetching during the build command

--
MOS_MIGRATED_REVID=93639664
diff --git a/src/main/java/com/google/devtools/build/lib/pkgcache/PackageCacheOptions.java b/src/main/java/com/google/devtools/build/lib/pkgcache/PackageCacheOptions.java
index f9d3efc..6db7cf6 100644
--- a/src/main/java/com/google/devtools/build/lib/pkgcache/PackageCacheOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/pkgcache/PackageCacheOptions.java
@@ -139,4 +139,10 @@
       category = "undocumented",
       help = "Threshold for number of loaded packages before skyframe-m1 cache eviction kicks in")
   public int minLoadedPkgCountForCtNodeEviction;
+
+  @Option(name = "fetch",
+      defaultValue = "true",
+      category = "undocumented",
+      help = "Allows the command to fetch external dependencies")
+  public boolean fetch;
 }