Rework pg_service.conf handling to support SSL keys authentication

[nirvn]

This PR reworks the way we handle the presence of a pg_service.conf in the QField data directory (i.e. on Android /Android/data/ch.opengis.qfield/files/QField) to allow for immediate and future improvements.

The big change: instead of having postgres consume that service configuration file (most often drag and dropped via USB cable), QField will copy its content into a new pg_service.conf file living within the QField app's writable system directory. By doing this, we unlock the ability by QField to modify that pg_service.conf file at will (think QFieldCloud-provided services being written into that file when successfully logging into QFC).

Back to the present, the new handling is meant to unlock support for SSL keys authentication through the following logic:

• when a pg_service.conf file is detected, QField will scan for three keys: sslrootcert, sslcert, and sslkey;
• for each key, QField will capture the value and look for its associated file using the value as a relative file path to pg_services.conf;
• when a file is found, QField will copy the file into the above-mentioned app's writable system directory and will tweak its access permission to satisfy postgres / openssl;
• QField will then modify the pg_services.conf content for the services to point to the newly copied files.

This method allows us to support SSL authentication on Android in a way that allows for the users to share the same pg_services.conf content across desktop and Android.

[qfield-fairy]

🎉 Ta-daaa, freshly created APKs are available for 213468b: arm64-android

Other architectures

• arm-neon-android
• x64-android
• x86-android
• all access arm64-android
• all access arm-neon-android
• all access x64-android
• all access x86-android