[codex] Set Freebuff ad request user agent (#661) #675

Job	Run time
build-and-smoke-freebuff-windows	1m 57s
build-freebuff	1m 20s
e2e-startup	1m 2s
e2e-agent-startup	2m 27s
e2e-help-command	1m 6s
e2e-terminal-command	1m 2s
e2e-slash-commands	59s
e2e-version	53s
e2e-ads-behavior	1m 11s
e2e-code-edit	1m 6s
	13m 3s

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