[codex] Add Moonshot Kimi backend provider #618

Job	Run time
build-and-smoke-freebuff-windows	2m 55s
build-freebuff	1m 5s
e2e-startup	1m 6s
e2e-ads-behavior	1m 18s
e2e-slash-commands	1m 7s
e2e-version	1m 10s
e2e-code-edit	58s
e2e-agent-startup	2m 20s
e2e-help-command	1m 15s
e2e-terminal-command	56s
	14m 10s

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