Implement Cassandra DB & PHP Extension (#2214)

* Implementing Cassandra DB & PHP Extension
* Update documentation for Cassandra
* Added Cassandra for testing CI

php-worker/Dockerfile

@@ -85,6 +85,26 @@ RUN if [ ${INSTALL_AMQP} = true ]; then \
     docker-php-ext-install sockets \
 ;fi
 
+# Install Cassandra drivers:
+ARG INSTALL_CASSANDRA=false
+RUN if [ ${INSTALL_CASSANDRA} = true ]; then \
+  apk --update add cassandra-cpp-driver \
+  ;fi
+
+WORKDIR /usr/src
+RUN if [ ${INSTALL_CASSANDRA} = true ]; then \
+  git clone https://github.com/datastax/php-driver.git \
+  && cd php-driver/ext \
+  && phpize \
+  && mkdir -p /usr/src/php-driver/build \
+  && cd /usr/src/php-driver/build \
+  && ../ext/configure --with-php-config=/usr/bin/php-config7.1 > /dev/null \
+  && make clean >/dev/null \
+  && make >/dev/null 2>&1 \
+  && make install \
+  && docker-php-ext-enable cassandra \
+;fi
+
 # Install Phalcon ext
 ARG INSTALL_PHALCON=false
 ARG PHALCON_VERSION