Draft: Switch from Sailfish's provisioning plugin to upstream's MBPI one, and make it merge APNs with the same value

Building upon !13 (merged), makes MBPI provisioning plugin merges contexts with the same APN value into 1, combined contexts. This should allow using MMS on networks which use the same APN for both internet and MMS - automatically if mobile-broadband-provider-info has the correct information.

However, MBPI doesn't always have the correct information. So it's still an open discussion at the moment whether we should use upstream MBPI, Sailfish's fork of MBPI (which @Flohack74 said will "always have heavily outdated data" [1], but I doubt), or LineageOS's apns-conf.xml (require a bit of effort to bring ubuntu-provision plugin back).

[1] ubports/development/core/focal-projectmanagement-missing-packages#77 (closed)