Command line non-username/password auth flow

**Is your feature request related to a problem? Please describe.**
Salesforce is deprecating ALL username/password API auth flows in the next year. OAuth username/pw will be gone by Winter '27 and SOAP login() will be gone by Summer '27. Data Loader command line does not, as far as I can tell, have any documented support for an alternate auth flow.

**Describe the solution you'd like**
Ideally OAuth Client Credentials would be perfect. We could just create an ECA in the org, register the client id/secret with the Data Loader command-line config and off to the races. Alternately Data Loader command-line would need a way of taking us through a web authentication flow and saving the appropriate auth data upon completion, so that it could be used in subsequent command-line executions.

**Describe alternatives you've considered**
We could migrate the customer to a completely different tool but this would be a headache.

**Additional context**
https://help.salesforce.com/s/articleView?id=release-notes.rn_security_unpw_flow_retirement.htm&release=262&type=5
_In Winter ’27, we'll stop supporting the OAuth 2.0 username-password flow for connected apps. This update will break all connected app integrations that use this flow. For better security, update your integrations to use the OAuth 2.0 web-server flow or the OAuth 2.0 client credentials flow instead._

https://help.salesforce.com/s/articleView?id=005132110&type=1
SOAP login() call is being retired with the Summer '27 release circa May 2027