Update schema to not require `client_secret`

[MartinFlores751]

Looking at the code using client_secret, we may be able to remove client_secret from the required portion of the schema:

irods_client_http_api/core/src/main.cpp

Lines 273 to 282 in 486c1b1

	"required": [
	"timeout_in_seconds",
	"state_timeout_in_seconds",
	"provider_url",
	"client_id",
	"require_aud_member_from_introspection_endpoint",
	"user_mapping",
	"client_secret",
	"access_token_validation_method"
	]

client_secret should only be required when access_token_validation_method is set to introspection.

Originally posted by @MartinFlores751 in #472