Add wallets/bitcoind submodule

We use the same bitcoind regtest module in Bisq 1 and 2. To avoid
duplicate code I moved the bitcoind module to its own repository.

.github/workflows/build_bisq_module.yml

@@ -20,6 +20,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/[email protected]
+        with:
+          submodules: 'true'
 
       - name: Setup Java JDK
         uses: actions/[email protected]
@@ -33,4 +35,4 @@ jobs:
           arguments: build -x test
           build-root-directory: ${{ inputs.build-root-dir }}
           gradle-executable: ./gradlew
-          gradle-version: 8.9
+          gradle-version: 8.9

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "wallets/bitcoind"]
+	path = wallets/bitcoind
+	url = https://github.com/bisq-network/bitcoind.git