ini/unstable: Add option to collect repeated key/values into arrays

[josh-hemphill]

Is your feature request related to a problem? Please describe.

Most of the config standards I work with that use ini-based configs all have repeated key/value entries for various options, and with the removal of IniMap in the unstable versions, there won't be a good option for parsing those ini's using a package on JSR.

Describe the solution you'd like

A simple option

Describe alternatives you've considered

Staying on the old version

[timreichen]

Could you give a code example and how it should be handled in your opinion?