fix: move git initialization to function body (#521)

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# Description
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illustrations where appropriate. -->
Import git module will fail when the execution environment does not
contain git executable. As Merlin SDK does not strictly rely on git, we
should move the import to the function body where it is needed instead.

# Modifications
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# Tests
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- [ ] Deploying PyFunc models
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# Checklist
- [ ] Added PR label
- [ ] Added unit test, integration, and/or e2e tests
- [ ] Tested locally
- [ ] Updated documentation
- [ ] Update Swagger spec if the PR introduce API changes
- [ ] Regenerated Golang and Python client if the PR introduces API
changes

# Release Notes
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```release-note
Fix a bug in which pyfunc related functions will fail when the execution environment does not have git executable.
```

python/sdk/merlin/pyfunc.py

@@ -10,7 +10,6 @@
 import pandas
 from caraml.upi.v1 import upi_pb2
 from docker import APIClient
-from git import Repo
 from merlin.docker.docker import copy_pyfunc_dockerfile, wait_build_complete
 from merlin.protocol import Protocol
 from merlin.version import VERSION
@@ -516,6 +515,10 @@ def run_pyfunc_local_server(
 
 
 def _clone_merlin_repo(context_path: str):
+    # Can't be imported at module level because the initialization will fail when the git executable
+    # does not exists.
+    from git import Repo
+
     repo_url = "https://github.com/caraml-dev/merlin.git"
     repo_path = f"{context_path}/merlin"
     if not os.path.isdir(repo_path):