[Bug]: filename containing invalid characters to be used as docker image name

[sonichi]

Describe the bug

https://github.com/microsoft/autogen/actions/runs/7338570361/job/19981290015?pr=925

The first line in the python block is:
# filename: inequality.py (you can choose your own filename)
The filename is parsed as inequality.py (you can choose your own filename) by:

autogen/autogen/agentchat/conversable_agent.py

Line 1121 in d583ad8

filename = code[11 : code.find("\n")].strip()

It then causes the error in

autogen/autogen/code_utils.py

Lines 401 to 402 in d583ad8

	tag = filename.replace("/", "")
	container.commit(repository="python", tag=tag)

Steps to reproduce

call
execute_code(filename="inequality.py (you can choose your own filename", use_docker=True, code="")

Expected Behavior

An error like https://github.com/microsoft/autogen/actions/runs/7338570361/job/19981290015?pr=925 should occur
at

autogen/autogen/code_utils.py

Lines 401 to 402 in d583ad8

	tag = filename.replace("/", "")
	container.commit(repository="python", tag=tag)

Screenshots and logs

https://github.com/microsoft/autogen/actions/runs/7338570361/job/19981290015?pr=925

Additional Information

AutoGen Version: 0.2.2

[ekzhu]

Related to #1095. The input filename should be validated and the docker image name should be validated