docs: update AssistantAgent documentation with a new figure, attentio… #3623

Job	Run time
check-proto-changes-python	1m 20s
docs (./packages/autogen-core)	1m 35s
format	53s
docs-example-check (./packages/autogen-core)	2m 46s
lint	1m 2s
markdown-code-lint	2m 20s
mypy (./packages/autogen-core)	2m 39s
mypy (./packages/autogen-magentic-one)	1m 31s
pyright (./packages/autogen-core)	1m 7s
mypy (./packages/agbench)	56s
samples-code-check	53s
pyright (./packages/autogen-magentic-one)	1m 2s
mypy (./packages/autogen-ext)	2m 0s
pyright (./packages/agbench)	58s
test (./packages/autogen-core)	57s
pyright (./packages/autogen-ext)	1m 9s
mypy (./packages/autogen-agentchat)	1m 25s
test (./packages/autogen-magentic-one)	2m 4s
pyright (./packages/autogen-agentchat)	1m 11s
mypy (./packages/magentic-one-cli)	1m 32s
test (./packages/autogen-ext)	3m 45s
pyright (./packages/magentic-one-cli)	55s
test (./packages/autogen-agentchat)	1m 19s
codecov (./packages/autogen-core)	12s
codecov (./packages/autogen-magentic-one)	10s
codecov (./packages/autogen-ext)	8s
codecov (./packages/autogen-agentchat)	13s
	36m 2s

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