Mach-composer

- Update build process to include arm docker images

- Major rewrite to move to a plugin based system. The plugins are for now all
built-in and part of the mach composer release but will in the future be
moved to external plugins.
- Use `go-git` to retrieve the git log instead of executing `git` directly. This
fixes (188)
- Remove panic() calls in the codebase and handle errors properly by printing
them to stdout and setting correct exit code
- Re-implement the `$(include())` syntax for include a separate components file
for the 2.0 versione (115)
- Fix rendering of variables in the generated terraform output (194)
- Fix a yaml parsing bug which resulted in not being able to disable management
of commercetools stores. (193)
- Escape backslashes for strings in HCL (133)

- Fix windows version due to wrong handling of the path separator (182)
- Restore the `sites` subcommand to output the sites in the config (178)
- Restore the `components` subcommand to output the components in the config (179)
- Support only passing one config file and use `main.yml` as default for now (177)

- Fixed inconsistencies between 1.2 and 2.x:
- Add `branch` option to component definitions to be able to perform a
`mach-composer update` and stay within a certain branch (during development)
- Fixed commercetools `stores` definitions
- Fixed bug where custom AWS and Azure provider version definitions weren't picked up

- Fixed inconsistencies between 1.2 and 2.x:
- Upgrade Terraform providers in golang version of the MACH composer to match the 1.2 release:
- Upgraded commercetools provider to 0.30.0
- Upgraded Amplience provider to 0.3.7
- Upgraded Azure provider to 2.99.0
- Add `variables_file` option to the `mach_composer` configuration block to define a variable file
- Fix auto add cloud integration (aws or azure) when `integration` list is left empty
- Add ability to define a custom provider version including the version operator
- Deprecate `commercetools.frontend` block, will be removed in a later release.

- Don't crash when running `mach-composer apply` without `--auto-approve`