add terminus secrets manager plugin

Author: kurowski

Dockerfile

@@ -36,8 +36,10 @@ RUN echo 'xdebug.log_level = 0' >> /usr/local/etc/php/conf.d/xdebug.ini
 RUN sed -i 's/Listen\s*80$/# Listen 80/' /etc/apache2/ports.conf
 
 # Install terminus
-RUN curl -L https://github.com/pantheon-systems/terminus/releases/latest/download/terminus.phar --output /usr/local/bin/terminus
-RUN chmod +x /usr/local/bin/terminus
+RUN curl -L https://github.com/pantheon-systems/terminus/releases/latest/download/terminus.phar --output /usr/local/bin/terminus \
+  && chmod +x /usr/local/bin/terminus \
+	&& terminus self:plugin:install terminus-secrets-manager-plugin
+
 
 # Install atuin
 #