Use static keystore for signing Android builds

Fixes #22861

GitHub Actions CI uses ephemeral debug keystore resulting in APKs being
signed differently each time. This results in user not having trust in
where the builds come from and Android rejecting the update due to
mismatched keys.

This commit introduces a script to (re)create a keystore to be used for
signing APKs in GitHub Actions, sets environment variables for CI job
with generated key and modifies gradle project to consume those
variables.

I have generated the keystore with aforementioned script and set
secrects in the main repository with both the keystore password and
keystore contents.

.github/workflows/ci.yml

@@ -613,6 +613,11 @@ jobs:
         uses: hendrikmuhs/ccache-action@v1.2.18
         with:
           key: android
+      - name: Setup keystore
+        run: |
+          echo "${{ secrets.OPENRCT2_KEYSTORE_CONTENTS }}" | base64 -d > keystore.jks
+          echo "OPENRCT2_KEYSTORE_FILE=${{ github.workspace }}/keystore.jks" >> $GITHUB_ENV
+          echo "OPENRCT2_KEYSTORE_PASSWORD=${{ secrets.OPENRCT2_KEYSTORE_PASSWORD }}" >> $GITHUB_ENV
       - name: Install GCC problem matcher
         uses: ammaraskar/gcc-problem-matcher@master
       - name: Build OpenRCT2