added dockerfile for postgis image

.gitlab-ci.yml

+stages:
+  - build_postgis
+
+build_image_postgis:
+  image: docker:stable-git
+  stage: build_postgis
+  variables:
+    DOCKER_HOST: tcp://docker:2375/
+    DOCKER_DRIVER: overlay2
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u $CI_REGISTRY_USER -p $CI_JOB_TOKEN git.steelkiwi.com:5005
+  script:
+    - echo "$IMAGE:$CI_JOB_ID" > images
+    - docker build --cache-from $IMAGE:cache -t $IMAGE:latest -f postgis/Dockerfile_develop .
+    - docker push $IMAGE:latest
+  only:
+    - postgis
+  tags:
+    - django_tests
\ No newline at end of file

postgis/Dockerfile

+FROM postgres:10-alpine
+MAINTAINER SteelKiwi Inc.
+
+ENV POSTGIS_VERSION 2.5.2
+
+RUN set -ex && apk --update add --no-cache \
+               --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing \
+               --virtual .packages \
+               make \
+               geos-dev \
+               proj4-dev \
+               gdal-dev \
+               json-c-dev \
+               g++ \
+               perl \
+               libxml2-dev
+
+RUN set -ex && mkdir /tmp/postgis \
+            && wget -O postgis.tar.gz "https://download.osgeo.org/postgis/source/postgis-$POSTGIS_VERSION.tar.gz" \
+            && tar --extract \
+                   --file postgis.tar.gz \
+                   --directory /tmp/postgis \
+                   --strip-components 1 \
+            && rm postgis.tar.gz \
+            && cd /tmp/postgis \
+            && ./configure \
+            && make \
+            && make install \
+            && rm -rf /tmp/postgis \
+            && apk del .packages
+
+RUN set -ex && apk add --no-cache \
+               --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing \
+               geos \
+               proj4 \
+               gdal \
+               json-c \
+               libxml2
+
+COPY ./postgis.sh /docker-entrypoint-initdb.d/postgis.sh
\ No newline at end of file

postgis/postgis.sh

+#!/usr/bin/env sh
+
+set -e
+
+export PGUSER="$POSTGRES_USER"
+
+psql <<- EOSQL
+		CREATE EXTENSION IF NOT EXISTS postgis;
+		CREATE EXTENSION IF NOT EXISTS postgis_topology;
+EOSQL
\ No newline at end of file