Mount Android keystores

[snoopdouglas]

This is to enable Android exports. Though it'd be possible by adding volumes and a pre-script in the config, it'd be ugly - far better to do it automatically.

We'll need to interrogate two files for this: export_presets.cfg, which can override per preset, and the user's editor_settings*.tres.

In the case of nothing being set up in the user environment, don't throw an error - this'll be a likely scenario in CI. A keystore is more likely to be pre-configured for Godot on a workstation because of one-click deploy.

Note we'll possibly want to consider this for other export fields which require things strewn around the FS.

[snoopdouglas]

Edit this won't work, as we need the user and password too.

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Scrap that, I'm just going to provide well-known locations instead. This should reduce complexity all round, at the cost of a bit of magic (some would say this is 100% a good thing).

In the docs, we'll suggest users mount keys like:

• ...:/srv/android/debug.keystore:ro
• ...:/srv/android/release.keystore:ro

[snoopdouglas]

nb. keystore path and user/pass overrides are stored in src/.godot/export_credentials.cfg.