Enable ES to save unique config entries based on relative path

[udance4ever]

Summary

Enables ES to save unique configs based on relative path and handle 2 cases:

1. Software with multiple media formats (eg. disk and cassette) (Batocera user config does not hash on both softName and media Type batocera.linux#11781)
2. Multiple MAME rom sets (MAME, MAME2010, MAME2003+)

PR is to be paired with a 1 line change to Emulator.py (batocera-linux/batocera.linux#12038) so entries in this format can be parsed by configgen on rom launch.

Examples

coco["zonx.zip"].altromtype=flop1
coco["cas/zonx.zip"].altromtype=cass

and

mame["cryptklr.zip"].core=mame
mame["cryptklr.zip"].emulator=mame
mame["mame2010/cryptklr.zip"].core=mame0139
mame["mame2010/cryptklr.zip"].emulator=libretro

Custom ES build

Successfully built using README in this repo (but not usable in Batocera)

What is the proper procedure to build only batocera-emulationstation? Instructions in our wiki got me running with a build container but did not allow me to build just Batocera ES with the proper flags and patches.