fix: fetch the registry's `main` branch in the monorepo Docker image (#3841)

### Description

Infra services require the presence of a registry. This is expected to
be found at the env var REGISTRY_URI. This PR fetches the latest
registry from `main` and uses that as the registry in the monorepo image
for infra services / scripts to make use of. To prevent caching of this
git clone, we use a build-time arg such that if the arg changes, any
later layers in the image will be ran. See
https://stackoverflow.com/a/73501716

### Drive-by changes

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Are there any minor or drive-by changes also included?
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### Related issues

- Partially fixes
https://github.com/hyperlane-xyz/hyperlane-monorepo/issues/3827 - we'll
need a deploy to fully close it out

### Backward compatibility

<!--
Are these changes backward compatible? Are there any infrastructure
implications, e.g. changes that would prohibit deploying older commits
using this infra tooling?

Yes/No
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### Testing

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What kind of testing have these changes undergone?

None/Manual/Unit Tests
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.github/workflows/monorepo-docker.yml

@@ -8,6 +8,8 @@ on:
     paths:
       # For now, because this image is only used to use `infra`, we just build for infra changes
       - 'typescript/infra/**'
+      - 'Dockerfile'
+      - '.dockerignore'
 concurrency:
   group: build-push-monorepo-${{ github.ref }}
   cancel-in-progress: true
@@ -74,3 +76,6 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+          # To always fetch the latest registry, we use the date as the cache key
+          build-args: |
+            REGISTRY_CACHE=${{ steps.taggen.outputs.TAG_DATE }}

Dockerfile

@@ -27,3 +27,10 @@ COPY typescript ./typescript
 COPY solidity ./solidity
 
 RUN yarn build
+
+ENV REGISTRY_URI="/hyperlane-registry"
+# To allow us to avoid caching the registry clone, we use a build-time arg to force
+# the below steps to be re-run if this arg is changed.
+ARG REGISTRY_CACHE="default"
+
+RUN git clone https://github.com/hyperlane-xyz/hyperlane-registry.git "$REGISTRY_URI"