fix: advertise support for response_mode=form_post in OIDC discovery document #1952

Job	Run time
Run OIDC conformity tests	8m 18s
Generate SDKs	3m 43s
Run HSM tests	4m 54s
Run tests and lints	5m 38s
Run end-to-end tests (memory)	5m 0s
Run end-to-end tests (memory, --jwt)	5m 2s
Run end-to-end tests (postgres)	4m 54s
Run end-to-end tests (postgres, --jwt)	5m 3s
Run end-to-end tests (mysql)	5m 13s
Run end-to-end tests (mysql, --jwt)	5m 23s
Run end-to-end tests (cockroach)	5m 23s
Run end-to-end tests (cockroach, --jwt)	5m 23s
Build CLI docs	0s
Generate changelog	0s
Generate release	0s
Draft newsletter	0s
Release SDKs	0s
Render version schema	0s
Send newsletter	0s
Pending approval Slack notification	0s
	1h 3m 54s

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