Allow importing extra config

[ruslandoga]

Changes

This PR allows importing extra config as suggested in #3705 (comment)

It can serve as an easy escape hatch for specifying configurations not covered by env vars. Like #3823

Example:

_{my_config.exs}

import Config

config :plausible, Plausible.Repo,
  after_connect: {Postgrex, :query!, ["SET search_path TO global_prefix", []]}

_{docker-compose.yml}

plausible:
  image: ghcr.io/plausible/community-edition:v2.1.0
+ volumes:
+   - ./my_config.exs:/app/my_config.exs

_{plausible-conf.env}

+ EXTRA_CONFIG_PATH=/app/my_config.exs

Tests

• Automated tests have been added

Changelog

• Entry has been added to changelog

Documentation

• document extra config community-edition#107

Dark mode

• This PR does not change the UI

[ruslandoga]

We are copying all rel/ files directly, the tar archive ends up being unused.

[ruslandoga]

This intermediate config file is needed as runtime.exs is forbidden from importing other configs

[ruslandoga]

From https://hexdocs.pm/mix/Mix.Tasks.Release.html#module-runtime-configuration

It MUST NOT import any other configuration file via import_config

[ruslandoga]

This is part of the default applications

[ruslandoga]

I've also tried it out locally:

docker run --rm -d \
    -v ./my_config.exs:/app/my_config.exs \
    -e EXTRA_CONFIG_PATH=my_config.exs \
    -e BASE_URL=http://localhost:8000 \
    -e SECRET_KEY_BASE=FQ9iAQSkUx4peZfjRT9AIcX2iUupTYIPH90GbRS42NDUYQUcVzaTEARzK8NBRpVO \
    -e TOTP_VAULT_KEY=ykRRyEnKQX8jJ0zrE3rn91U0jluSsnevOGnQO2fTYUg= \
    -e DATABASE_URL=ecto://postgres:postgres@172.17.0.2:5432/plausible_dev \
    -e CLICKHOUSE_DATABASE_URL=http://172.17.0.3:8123/plausible_events_db \
    plausible:local

$ ls
bin                      erts-14.2.1              init-admin.sh            migrate.sh               pending-migrations.sh    rollback.sh
createdb.sh              import_extra_config.exs  lib                      my_config.exs            releases                 seed.sh
$ cat my_config.exs 
import Config

config :plausible, Plausible.Repo,
  after_connect: {Postgrex, :query!, ["SET search_path TO public", []]}

config :plausible, a: :b
$ bin/plausible remote
Erlang/OTP 26 [erts-14.2.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Interactive Elixir (1.16.0) - press Ctrl+C to exit (type h() ENTER for help)

iex(plausible@7f241994598d)1> Application.get_env :plausible, Plausible.Repo
[
  timeout: 300000,
  connect_timeout: 300000,
  handshake_timeout: 300000,
  url: "ecto://postgres:postgres@172.17.0.2:5432/plausible_dev",
  socket_options: [],
  ssl_opts: [
    cacertfile: "/app/lib/castore-1.0.5/priv/cacerts.pem",
    verify: :verify_peer,
    customize_hostname_check: [
      match_fun: #Function<6.117093159/2 in :public_key.pkix_verify_hostname_match_fun/1>
    ]
  ],
  after_connect: {Postgrex, :query!, ["SET search_path TO public", []]}
]
iex(plausible@7f241994598d)2> Application.get_env :plausible, :a
:b

[ruslandoga]

I couldn't come up with a simple test that would check that extra config overrides runtime.exs, but it does.