Add mod_rewrite to Docker image httpd:alpine

mod_rewrite is installed by default with apache in alpine, so no need to install it again. So here's how you enable mod_rewrite in Alpine:

FROM httpd:alpine

# Copy .htaccess into DocumentRoot
COPY ./.htaccess /var/www/html/

RUN sed -i '/LoadModule rewrite_module/s/^#//g' /usr/local/apache2/conf/httpd.conf

RUN { \
  echo 'IncludeOptional conf.d/*.conf'; \
} >> /usr/local/apache2/conf/httpd.conf \
  && mkdir /usr/local/apache2/conf.d