a bit

- make gunicorn workers and threads configurable by environment
  variables,
- make gunicorn report metrics to statds

to prevent cases where the upstream server IP has changed (reload,
rescaling, etc.) but nginx still uses the old (cached) IP.

we do want the main swh command to receive SIGTERM from docker so it
does gracefully disconnect the kafka consumer, thus properly leave the
consumer group.

This prevents from having to wait for the kafka server to figure that a
client actually left the consumer group before rebalancing the
partitions.

TL;DR: allows to make a restart/rescaling of the replayers much
faster.

and improve the swh-wen entrypoint.

The orgname only scheme requires to be registered as "official image",
which we may want to be at some point, but not ready yet.

https://docs.docker.com/docker-hub/official_images/

- merge Dockerfiles into a single one using multistage build
- create a replayer-specific image
- add `name:` to configs so it's a bit easier to deploy a config update
  (well it's sure a bit easier to document this actually),
- add missing wait-for-it statements in replayer/entrypoint.sh

The reason for the docker image renaming is to make it easier to
organise software heritage images on the docker hub; we now have only
one "entrypoint".

swh-storage now support several db flavors (default, mirror, replica)
and `swh db` has now separate tools for the db creation and the db
initialization.

Modify the entrypoint/helper tools in the base image accordingly.

Also improve the README file.

- Use 'docker-compose config' to generate the merged compose file
  since 'docker [stack] deploy' is buggy.
- Use 'docker stack deploy' instead of the experimental 'docker deploy'
  command directly.
- Remove all the remote/by-topic example files; these are confusing.

This changes also the way the (storage) database is initialized: it now
checks whether the db exists and is initilized before attempting to
execute the `swh db init` tool.

The added fix_storage_for_mirror shell function executes a small sql
script that remove any constraint that can prevent the mirror storage
from working.

To publish built images, you now need to specify it using:

  PUBLISH=yes ./build_images.sh

from the images/ directory.

to select the swh images to use, like:

  image: softwareheritage/base:${SWH_IMAGE_TAG:-latest}

Also add example config files for the graph-replayer-remote-bytopic.yml
replayer config.

It build docker images with curent datetime as tag and upload them to
the docker's hub if docker's current user is 'softwareheritage'.

It will build images like:

  softwareheritage/base:20200819-112604
  softwareheritage/web:20200819-112604

Note that both images (base and web) will have the same datestamp.

idea is be able to easily rebuild the images including latest swh packages
using docker image cache (prevent from having to run "docker build --no-cache").

where replayer code has been moved.

as required by recent swh-web versions.

use a proxied access to the prometheus server so it does not need the
user's browser to have direct access to the prometheus nor nginx container.

prevent collision with dev environment docker setup.

this allows to execute directly shell commands without the need for an
interactive session.

by not installing recommended debian packages.

- activate statsd reporting in all services,
- split the content-replayer service by type/topic