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

these are needed in recent swh-web versions.

- add a section on how to update a service,
- add a note on activation of experimental features of docker,
- fixes and typos.