Deprecation: remove code for config file v1 and default config file (#10367)

* Deprecation: remove code for config file v1 and default config file

This is a continuation of the work done for

* #10351
* #10342
* #10348
* #10355

In that work we added notifications, warning messages and finally a feature flag
to start failing the builds without a configuration file or using v1.

This commit removes all the code for config file v1 and building without a
configuration file. Due to that, it also removes the code that allows users to
use the older Docker images (testing, latest, stable)

This work can be merged once we enable the feature flag to fail the builds for
all the projects and we are happy with the results.

* Deprecation: update documentation of config file

* Deprecation: update config file to remove old keys

* Deprecation: update config file v2 docs to deprecate keys

- python.version
- python.system_packages

People should not be using these keys.

* Remove auto-install requirements file found on project

* Make the deprecated fields read-only as discussed

* Remove tasks to send emails about deprecations

* Lint & Tests

* Remove reference to v1 config file docs

* Normalize `get_build_config()`

* Update tests for config file

* Update tests for collectors

* Update tests to follow the new deprecations

* Remove invalid tests

* More updates related to the config files

* Update more tests

* Lint

Author: humitos