Add support for entrypoint attribute

[davidkopp]

Closes #1085

Only the short form of the entrypoint attribute is implemented (see Docker Compose specification).
This is also the case for the `command' attribute, where only the short form is currently implemented.

Greptile Summary

Added support for Docker entrypoint attribute in service configurations, allowing overriding of predefined container ENTRYPOINTs to enable execution of runtime commands in test flows.

• Added entrypoint validation in lib/schema_checker.py as an optional string field in service definitions
• Added test_entrypoint_ran() in tests/test_usage_scenario.py to verify entrypoint command execution
• Modified runner.py to support entrypoint attribute using secure command parsing via shlex.split()
• Added test scenario entrypoint_stress.yml demonstrating entrypoint usage with stress testing commands

The implementation enables use of common API/load testing tools like JMeter, k6, Artillery and grpcurl that have predefined ENTRYPOINTs.

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[ArneTR]

Uh, this looks juicy, ty!

1. I will let our GreptileAI check it ... so beware for maybe incoming comments.
2. On first view I believe using shlex.split on the entrypoint may introduce an argument injection. The idea is to have whatever is supplied as entrypoint to be supplied as one contigous string.
   => I will give it a more thorough look tomorrow morning

First and foremost: Big thx!

[ArneTR]

@greptileai

[greptile-apps]

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[greptile-apps]

logic: entrypoint should be added before any docker-run-args to match Docker's behavior where entrypoint is processed before additional arguments

[greptile-apps]

style: verify that entrypoint is not empty or None before extending docker_run_string

Suggested change

	if 'entrypoint' in service:
	docker_run_string.extend(shlex.split(service['entrypoint']))
	if 'entrypoint' in service and service['entrypoint']:
	docker_run_string.extend(shlex.split(service['entrypoint']))

[greptile-apps]

style: check that entrypoint is a string type before calling shlex.split()

Suggested change

	if 'entrypoint' in service:
	docker_run_string.extend(shlex.split(service['entrypoint']))
	if 'entrypoint' in service and isinstance(service['entrypoint'], str):
	docker_run_string.extend(shlex.split(service['entrypoint']))

[greptile-apps]

style: Consider adding validation to ensure entrypoint doesn't contain shell syntax that could be unsafe (similar to contains_no_invalid_chars check)

Suggested change

	Optional("entrypoint"): And(str, Use(self.not_empty)),
	Optional("entrypoint"): And(str, Use(self.not_empty), Use(self.contains_no_invalid_chars)),

[davidkopp]

My initial implementation was completely wrong. Sorry for that.
Before marking the PR as ready I would like to do some more tests. For example I would like to set the entrypoint to entrypoint.sh to be able to execute arbitrary commands instead of just one word.

[davidkopp]

I think the PR is now ready for review. I added now 3 unit tests in total to have a good understanding of how the entrypoint can be used, also in conjunction with command.
Let me know, if 3 tests are too much because of the time the tests are taking.

I didn't do the changes greptile proposed, because then it would not be consistent with the rest of the code.