* Add a development container config for VS Code

This creates a development environment with a FoundationDB server
and a CouchDB layer in two containers, sharing a network through
Docker Compose.

It uses the FDB image published to Docker Hub for the FDB container,
and downloads the FDB client packages from foundationdb.org to provide
the development headers and libraries. www.foundationdb.org is actually
not trusted in Debian Buster by default, so we have to download the
GeoTrust_Global_CA.pem. The following link has more details:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=962596

Once the Docker Compose setup is running, VS Code executes the
create_cluster_file.bash script to write down a cluster file containing
the IP address in the compose network where the FDB service can be
found. This cluster file is used both for a user-driven invocation of
`./dev/run`, as well as for unit tests that require a running CouchDB.

Additionally, I've got a small fix to the way we run explicitly specified
eunit tests:

* Run eunit tests for each app separately

The `eunit` target executes a for loop that appears intended to use a
separate invocation of rebar for each Erlang application's unit tests.
When running `make eunit` without any arguments this works correctly,
as the for loop processes the output of `ls src`. But if you specify a
comma-delimited list of applications the for loop will treat that as a
single argument and pass it down to rebar. This asymmetry is
surprising, but also seems to cause some issues with environment
variables not being inherited by the environment used to execute the
tests for the 2..N applications in the list. I didn't bother digging
into the rebar source code to figure out what was happening there.

This patch just parses the incoming comma-delimited list with `sed` to
create a whitespace-delimited list for the loop, so we get the same
behavior regardless of whether we are specifying applications
explicitly or not.

* Simplify and speedup dev node startup

This patch introduces an escript that generates an Erlang .boot script
to start CouchDB using the in-place .beam files produced by the compile
phase of the build. This allows us to radically simplify the boot
process as Erlang computes the optimal order for loading the necessary
modules.

In addition to the simplification this approach offers a significant
speedup when working inside a container environment. In my test with
the stock .devcontainer it reduces startup time from about 75 seconds
down to under 5 seconds.

* Rename boot_node to monitor_parent

* Add formatting suggestions from python-black

Co-authored-by: Paul J. Davis <paul.joseph.davis@gmail.com>

New `elixir-suite` Makefile target is added. It runs a predefined set of elixir
integration tests.

The feature is controlled by two files:
- test/elixir/test/config/suite.elixir - contains list of all available tests
- test/elixir/test/config/skip.elixir - contains list of tests to skip

In order to update the `test/elixir/test/config/suite.elixir` when new tests
are added. The one would need to run the following command:

```
MIX_ENV=integration mix suite > test/elixir/test/config/suite.elixir
```

Since https://github.com/apache/couchdb-fauxton/pull/1299 only runtime
dependencies are installed when using 'npm install --production'.
To correctly build the Fauxton release, one must install all dependencies
with 'npm install'.

Update tests to use the new replicator. Also clean up redundancy and re-use
some of the newer macros from fabric2 (?TDEF_FE).

Make sure replicator tests are included in `make check`