feat(config): Mount config as a volume to Sentry (#407)

This follows the best-practice of mounting the config folder as a volume and removes the need to rebuild sentry images for config changes. Partially addresses #314.

sentry/Dockerfile

@@ -1,18 +1,7 @@
 ARG SENTRY_IMAGE
 FROM ${SENTRY_IMAGE:-getsentry/sentry:latest}
 
-WORKDIR /usr/src/sentry
-
-# Add WORKDIR to PYTHONPATH so local python files don't need to be installed
-ENV PYTHONPATH /usr/src/sentry
 COPY . /usr/src/sentry
 
 # Hook for installing additional plugins
 RUN if [ -s requirements.txt ]; then pip install -r requirements.txt; fi
-
-# Hook for installing a local app as an addon
-RUN if [ -s setup.py ]; then pip install -e .; fi
-
-# Hook for staging in custom configs
-RUN if [ -s sentry.conf.py ]; then cp sentry.conf.py $SENTRY_CONF/; fi \
-	&& if [ -s config.yml ]; then cp config.yml $SENTRY_CONF/; fi