enable edenapi push for integration tests

Summary:
# Context

The new AugmentedManifest format used by Sapling and Mononoke will support looking up Trees/Blobs from CAS via (Blake3,size) pairs. We already provide a way for users to get (Blake3,size) pairs for blobs, but there is currently no easy way to get this information for trees.

We want to add support to getAttributesFromFilesV2 for looking up the (Blake3,size) pairs for trees as well. To do this, we'll need to add a method for querying TreeMetadata (including size and Blake3 hashes) via the SaplingBackingStore.

This initial implementation of TreeMetadata will only include the following features:

1) Ability to query TreeMetadata from the SaplingBackingStore via a getTreeMetadata endpoint
2) The ability to request TreeMetadata from the getAttributesFromFilesV2 thrift endpoint

In the future, we will extend the implementation to support:

1) Automatically fetching TreeMetadata during BackingStore::getTree requests
2) Caching TreeMetadata in Eden's in-memory caches

# This diff

enables edenapi push for integration tests so that the readdir integration tests can push to an eagerepo and request TreeAuxData from the server afterwards

Reviewed By: quark-zju

Differential Revision: D59662772

fbshipit-source-id: 4cb6620abaf416693b6688b3314490ba35bc07aa

Author: MichaelCuevas

eden/integration/lib/hgrepo.py

@@ -307,6 +307,10 @@ def init(
         hgrc.setdefault("checkout", {})
         hgrc["checkout"]["use-rust"] = "true"
 
+        # It's safe to use EdenAPI push for testing purposes
+        hgrc.add_section("push")
+        hgrc["push"]["edenapi"] = "true"
+
         self.write_hgrc(hgrc)
 
         storerequirespath = os.path.join(self.path, ".hg", "store", "requires")
@@ -478,4 +482,5 @@ def push(self, rev: str, target: str, create: bool = False) -> str:
         args = ["push", "-r", rev, "--to", target]
         if create:
             args.append("--create")
+
         return self.hg(*args)