feat: support publishing to snowflake SPCS with token #3466
Description
The snowflake support added in #2632 no longer works since Connect switched from trusting Snowflake headers for user identification, to using OIDC. To publish to Connect running in SPCS we now require dual authentication, both Snowflake and Connect.
This issue is for adding dual auth with Connect tokens.
See https://connect.posit.it/snowflake/demo.html for the current address of the dogfood SPCS server, which we can use for development and testing.
This will only work when Publisher is not also running in SPCS (see #3226).