Add default_header support #4006

Job	Run time
format	1m 26s
lint	1m 2s
mypy (./packages/autogen-core)	3m 30s
mypy (./packages/autogen-magentic-one)	1m 28s
pyright (./packages/autogen-core)	1m 19s
test (./packages/autogen-core)	1m 2s
mypy (./packages/agbench)	1m 8s
pyright (./packages/autogen-magentic-one)	1m 21s
test (./packages/autogen-magentic-one)	1m 53s
pyright (./packages/agbench)	55s
mypy (./packages/autogen-ext)	3m 8s
test (./packages/autogen-ext)	25m 18s
mypy (./packages/autogen-agentchat)	1m 24s
pyright (./packages/autogen-ext)	1m 6s
pyright (./packages/autogen-agentchat)	57s
mypy (./packages/magentic-one-cli)	1m 21s
test (./packages/autogen-agentchat)	1m 5s
pyright (./packages/magentic-one-cli)	1m 9s
check-proto-changes-python	1m 16s
docs (./packages/autogen-core)	1m 38s
docs-example-check (./packages/autogen-core)	3m 21s
markdown-code-lint	2m 4s
samples-code-check	1m 27s
codecov	0s
	1h 0m 18s

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