Feature Type

I'm interested in functionality that solves a current problem or limitation in how CumulusCI works.

Does your feature request solve a current problem?

This change could be an easier change and first step to support multiple packages in a single repository without changing the structure of the cumulusci.yml file by multiple project support to it.

Describe the solution you'd like

Since sfdx supports multiple 2GP packages per repository in a single sfdx-project.json file, it would be nice if CumulusCI would provide a way to use different files for these packages.
I'd like to have support 2 types of override:

• env var CUMULUSCI_YML (or similar)
• --configFile <filename> option for any command, same level handling as --debug is Today.

Obviously this change could require deeper changes in git integration for get changes and such to filter git logs to a particular folder.
Perhaps implementation needs to find a way to support 1:1 mapping of "package aliases" and entries in sfdx-project.json, so instead (or beside) the filename override a --package <alias> could be used.

Describe alternatives you've considered

No alternatives, beside using multiple repositories, because this is how Cumulus CI was designed.

An alternative, more involved implementation could be to support a PROJECTS > <project alias> level to the YAML file and support specifying a project name on the command line. The structure below that node would be identical what is supported Today at the root level of the file.

Additional context

No response