Parse config CSV values as CSV

[aduth]

🛠 Summary of changes

Improves IdentityConfig converter for comma_separated_string_list to support CSV values embedding commas within double-quoted segments.

This is in response to a recent discovery that this was unsupported, which led to delays implementing a fix, and required a workaround in #10346 and patch deploy of RC 367.1. The changes included here could have avoided the need for that.

📜 Testing Plan

rspec spec/lib/identity_config_spec.rb

Validate compatibility of remaining uses of comma_separated_list_value:

• requests_per_ip_cidr_allowlist
• requests_per_ip_path_prefixes_allowlist
• test_ssn_allowed_list