docs: categorize APIs in docs/README.md #790

Job	Run time
build / build	1m 16s
run (oidcc-client-basic-certification-test-plan)	1m 33s
run (client_secret_basic, oidcc-client-test-plan)	1m 36s
run (client_secret_post, oidcc-client-test-plan)	1m 35s
run (request_object, oidcc-client-test-plan)	1m 33s
run (private_key_jwt, oidcc-client-test-plan)	1m 50s
run (none, oidcc-client-test-plan)	1m 41s
run (RS256, oidcc-client-test-plan, request_object, private_key_jwt)	1m 34s
run (RS384, oidcc-client-test-plan, request_object, private_key_jwt)	1m 36s
run (RS512, oidcc-client-test-plan, request_object, private_key_jwt)	1m 46s
run (PS256, oidcc-client-test-plan, request_object, private_key_jwt)	1m 44s
run (PS384, oidcc-client-test-plan, request_object, private_key_jwt)	1m 32s
run (PS512, oidcc-client-test-plan, request_object, private_key_jwt)	1m 30s
run (ES256, oidcc-client-test-plan, request_object, private_key_jwt)	1m 33s
run (EdDSA, oidcc-client-test-plan, request_object, private_key_jwt)	1m 35s
run (fapi2-security-profile-id2-client-test-plan)	2m 19s
run (fapi2-security-profile-id2-client-test-plan, plain_oauth)	1m 13s
run (fapi2-message-signing-id1-client-test-plan)	2m 52s
run (fapi2-message-signing-id1-client-test-plan, plain_oauth)	1m 52s
	32m 10s

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