added initial docker setup for running NGAS locally

ci/psql/Dockerfile.db-ngas

+FROM postgres:12.6-alpine
+
+ARG NGAS_VERSION=11.0.2
+
+WORKDIR /repos
+
+RUN apk add git && \
+    git clone --depth 1 --branch "v${NGAS_VERSION}" https://github.com/ICRAR/ngas.git && \
+    cp ngas/src/ngamsCore/ngamsSql/ngamsCreateTables-PostgreSQL.sql /docker-entrypoint-initdb.d/ngamsCreateTables-PostgreSQL.sql