[FR] Able to create firebase::AppOptions using a path to config file

Is there any way to load configs from GoogleService-Info.plist for multi projects?

Firebase's docs says
>If the builds are part of a single target, the best option is to give both configuration files unique names (e.g. GoogleService-Info-Free.plist and GoogleService-Info-Paid.plist). Then choose at runtime which plist to load.
at https://firebase.google.com/docs/projects/multiprojects

but firebase cpp sdk supports only json and we cannot download json for ios,
so it seems we have to generate json manually, set each properties by setter or replace plist by shell script.