Final Migration Step (#6)

* first migration steps
  * altered issue templates
  * altered README
  * removed .travis.yml
* adjusting registry & repository, Dockerfile and compose.env
* Close stale issues automatically
* Integrated CI with Github Actions (#3)
* feat: integrated ci with github actions
* fix: use secrets for docker org and update image
* docs: clarify why we use -t if no tty exists
* fix: correct remaining references to old repo
chore: prettier automatically updated markdown as well
* fix: hardcode docker org
* change testing image to just testing
* ci: add armv7 as a supported platform
* finished migration steps
* corrected linting in build-push action
* corrected linting in build-push action (2)
* minor preps for PR
* correcting push on pull request and minor details
* adjusted workflows to adhere closer to @wernerfred's diagram
* minor patches
* adjusting Dockerfile's installation of base packages
* adjusting schedule for stale issue action
* reverting license text
* improving CONTRIBUTING.md PR text
* Update CONTRIBUTING.md
* a bigger patch at the end
  * moved all scripts into one directory under target/scripts/
  * moved the quota-warning.sh script into target/scripts/ and removed empty directory /target/dovecot/scripts
  * minor fixes here and there
  * adjusted workflows for use a fully qualified name (i.e. docker.io/...)
  * improved on the Dockerfile layer count
  * corrected local tests - now they (actually) work (fine)!
  * corrected start-mailserver.sh to make use of defaults consistently
  * removed very old, deprecated variables (actually only one)
* various smaller improvements in the end
* last commit before merging #6
* rearranging variables to use alphabetic order

Co-authored-by: casperklein <casperklein@users.noreply.github.com>
Co-authored-by: Nick Pappas <radicand@users.noreply.github.com>
Co-authored-by: William Desportes <williamdes@wdes.fr>

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing
 
-`docker-mailserver` is OpenSource. That means that you can contribute on enhancements, bug fixing or improving the documentation in the Wiki.
+This project is Open Source. That means that you can contribute on enhancements, bug fixing or improving the documentation in the [Wiki](https://github.com/docker-mailserver/docker-mailserver/wiki).
 
 1. [Issues & PRs](#issues--prs)
    1. [Opening an Issue](#opening-an-issue)
@@ -23,20 +23,18 @@ You want to add a feature? Feel free to start creating an issue explaining what
 
 The development workflow is the following:
 
-- Fork the project and clone your fork
-- Create a branch using `git checkout -b branch_name` (you can use `issue-xxx` if fixing an existing issue)
-- Run `git submodule init` and `git submodule update` to get the BATS submodules
-- Code :-)
-- Add integration tests in `test/tests.bats`
-- Use `make clean all` to build image locally and run tests
-  Note that tests work on Linux only; they hang on Mac and Windows.
-- Document your improvements in `README.md` or Wiki depending on content
-- [Commit][commit], if possible with [signing your commit with a GPG key][gpg], push and make a pull-request
-- Pull-request is automatically tested on Travis
-- When tests are green, a review may be done
-- When changed are validated, your branch is merged into `master`
-- `master` is automatically tested on Travis
-- Docker builds a new `latest` image
+1. Fork the project and clone your fork
+   1. Create a new branch to work on
+   2. Run `git submodule update --init --recursive`
+2. Write the code that is needed :D
+3. Add integration tests if necessary
+4. Get the linters with `make install_linters`
+5. Use `make clean all` to build image locally and run tests (note that tests work on Linux **only**)
+6. Document your improvements if necessary (e.g. if you introduced new environment variables, write the description in [`ENVIRONMENT.md`](./ENVIRONMENT.md))
+7. [Commit][commit] and [sign your commit][gpg], push and create a pull-request to merge into `master`
+   1. Pull requests are automatically tested against the CI and will be reviewed when tests pass
+   2. When your changes are validated, your branch is merged
+   3. CI builds the new `:latest` image
 
 ## Coding Style