Publish doltgres Docker image on release

[coffeegoddd]

On release, publish a dolt/doltgresql Docker image.

[itdependsnetworks]

Was looking for this, just noting for myself as well as others, needed the following changes to work with my M1 mac to work with the PostgresDockerfile file.

diff --git a/testing/PostgresDockerfile b/testing/PostgresDockerfile
index cfe075d9..593ab122 100644
--- a/testing/PostgresDockerfile
+++ b/testing/PostgresDockerfile
@@ -1,4 +1,4 @@
-FROM --platform=linux/amd64 ubuntu:20.04
+FROM ubuntu:20.04

 # install python, java, bats, git ruby, perl, cpan
 ENV DEBIAN_FRONTEND=noninteractive
@@ -92,10 +92,14 @@ RUN bash ./build.sh

 # Build the doltgres binary, which we will need for bats, and put it on PATH
 WORKDIR /root/building/doltgresql/cmd/doltgres
+ENV CGO_ENABLED=1
+ENV GOOS=linux
+ENV GOARCH=arm64
+ENV CC=aarch64-linux-gnu-gcc
 RUN go build -o /usr/local/bin/doltgres .

 COPY ./testing/postgres-client-tests /postgres-client-tests
 COPY ./testing/postgres-client-tests/postgres-client-tests-entrypoint.sh /postgres-client-tests/entrypoint.sh