allow way to build a local generator image instead of relying of existing one

build.ps1

@@ -1,7 +1,12 @@
 # This script will run docker-compose-generator in a container to generate the yml files
-if (-not ($BTCPAYGEN_DOCKER_IMAGE)) { $BTCPAYGEN_DOCKER_IMAGE = "btcpayserver/docker-compose-generator" }
 
-docker pull $BTCPAYGEN_DOCKER_IMAGE:
+If (-not ($BTCPAYGEN_DOCKER_IMAGE)) { $BTCPAYGEN_DOCKER_IMAGE = "btcpayserver/docker-compose-generator" }
+If($BTCPAYGEN_DOCKER_IMAGE -eq "build"){
+	docker build docker-compose-generator --tag build
+} Else {
+	docker pull $BTCPAYGEN_DOCKER_IMAGE:
+}
+
 docker run -v "$(Get-Location)\Generated:/app/Generated" `
            -v "$(Get-Location)\docker-compose-generator\docker-fragments:/app/docker-fragments" `
            -e "BTCPAYGEN_CRYPTO1=$BTCPAYGEN_CRYPTO1" `

build.sh

@@ -1,7 +1,13 @@
 #!/bin/bash
 
+if [ "$BTCPAYGEN_DOCKER_IMAGE" == "build" ]
+then
+    docker build docker-compose-generator --tag build
+else
+    docker pull ${BTCPAYGEN_DOCKER_IMAGE:-"btcpayserver/docker-compose-generator"}
+fi
+
 # This script will run docker-compose-generator in a container to generate the yml files
-docker pull ${BTCPAYGEN_DOCKER_IMAGE:-"btcpayserver/docker-compose-generator"}
 docker run -v "$(pwd)/Generated:/app/Generated" \
            -v "$(pwd)/docker-compose-generator/docker-fragments:/app/docker-fragments" \
            -e "BTCPAYGEN_CRYPTO1=$BTCPAYGEN_CRYPTO1" \