Add logic to upload the Godot Android library to MavenCentral

Add environment variables to sign the release build for the Godot
Android editor and to publish the library to MavenCentral.
If the environment vars are not defined, we do a simple unsigned
`release_debug` build for the Android editor.

Change `config.sh.in` template to use single quotes by default, to
prevent expanding special characters in environment variables.

To publish to MavenCentral, a new `build-android/upload-mavencentral.sh`
script is added. It needs to run after the build using gradle, but we
still want it to be optional and used only when making an official
release, so we copy the compiled sources in the first step.

Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>

config.sh.in

@@ -3,16 +3,28 @@
 # Configuration file for user-specific details.
 # This file is gitignore'd and will be sourced by build scripts.
 
+# Note: For passwords or GPG keys, make sure that special characters such
+# as $ won't be expanded, by using single quotes to enclose the string,
+# or escaping with \$.
+
+# These scripts are designed and tested against podman. They may also work
+# with docker, but it's not guaranteed. You can set this variable to the
+# relevant tool in your PATH or an absolute path to run it from.
+export PODMAN='podman'
+
 # Registry for build containers.
 # The default registry is the one used for official Godot builds.
 # Note that some of its images are private and only accessible to selected
 # contributors.
 # You can build your own registry with scripts at
 # https://github.com/godotengine/build-containers
-export REGISTRY="registry.prehensile-tales.com"
+export REGISTRY='registry.prehensile-tales.com'
+
+# Version string of the images to use in build.sh.
+export IMAGE_VERSION='4.x-f36'
 
 # Default build name used to distinguish between official and custom builds.
-export BUILD_NAME="custom_build"
+export BUILD_NAME='custom_build'
 
 # Default number of parallel cores for each build.
 export NUM_CORES=16
@@ -21,28 +33,50 @@ export NUM_CORES=16
 # If you do not fill all SIGN_* fields, signing will be skipped.
 
 # Path to pkcs12 archive.
-export SIGN_KEYSTORE=""
+export SIGN_KEYSTORE=''
 
 # Password for the private key.
-export SIGN_PASSWORD=""
+export SIGN_PASSWORD=''
 
 # Name and URL of the signed application.
 # Use your own when making a thirdparty build.
-export SIGN_NAME=""
-export SIGN_URL=""
+export SIGN_NAME=''
+export SIGN_URL=''
 
-# Hostname or IP address of an macOS host (Needed for signing)
-# eg "user@10.1.0.10"
-export OSX_HOST=""
+# Hostname or IP address of an OSX host (Needed for signing)
+# eg 'user@10.1.0.10'
+export OSX_HOST=''
 # ID of the Apple certificate used to sign
-export OSX_KEY_ID=""
+export OSX_KEY_ID=''
 # Bundle id for the signed app
-export OSX_BUNDLE_ID=""
+export OSX_BUNDLE_ID=''
 # Username/password for Apple's signing APIs (used for atltool)
-export APPLE_ID=""
-export APPLE_ID_PASSWORD=""
+export APPLE_ID=''
+export APPLE_ID_PASSWORD=''
 
 # NuGet source for publishing .NET packages
-export NUGET_SOURCE="nuget.org"
+export NUGET_SOURCE='nuget.org'
 # API key for publishing NuGet packages to nuget.org
-export NUGET_API_KEY=""
+export NUGET_API_KEY=''
+
+# MavenCentral (sonatype) credentials
+export OSSRH_GROUP_ID=''
+export OSSRH_USERNAME=''
+export OSSRH_PASSWORD=''
+# Sonatype assigned ID used to upload the generated artifacts
+export SONATYPE_STAGING_PROFILE_ID=''
+# Used to sign the artifacts after they're built
+# ID of the GPG key pair, the last eight characters of its fingerprint
+export SIGNING_KEY_ID=''
+# Passphrase of the key pair
+export SIGNING_PASSWORD=''
+# Base64 encoded private GPG key
+export SIGNING_KEY=''
+
+# Android signing configs
+# Path to the Android keystore file used to sign the release build
+export GODOT_ANDROID_SIGN_KEYSTORE=''
+# Key alias used for signing the release build
+export GODOT_ANDROID_KEYSTORE_ALIAS=''
+# Password for the key used for signing the release build
+export GODOT_ANDROID_SIGN_PASSWORD=''