Gitlabform

* Fix another case of GitLab's Schedules API change/bug. Fixes [364](https://github.com/gitlabform/gitlabform/issues/364).

* **Allow breaking configuration inheritance**. Implements [326](https://github.com/gitlabform/gitlabform/issues/326). PR [#339](https://github.com/gitlabform/gitlabform/pull/339).

Imagine you have a configuration like this:
yaml
projects_and_groups:
my-group/*:
members:
enforce: true
groups:
regular-developers:
group_access: developer

my-group/special-private-project:
members:
inherit: false <--- the new keyword
enforce: true
groups:
special-developers:
group_access: developer
users:
john:
access_level: maintainer

With the new `inherit: false` entry used here, the effective members for `my-group/special-private-project` project are ONLY the `special-developers` grup and `john` user.

* Always expect pagination for GETs. Fixes [354](https://github.com/gitlabform/gitlabform/issues/354). PR [#358](https://github.com/gitlabform/gitlabform/pull/358).
* Workaround for the GitLab's Schedules API change/bug. Fixes [361](https://github.com/gitlabform/gitlabform/issues/361).

<br/>

Big thanks to the [Elastic Path](https://www.elasticpath.com/) team for their contribution of the above feature, especially [ep-linden](https://github.com/ep-linden) for the whole implementation and [amimas](https://github.com/amimas) for the initial proposal and cooperation on design!

<br/>

(There were 4 pre-releases of this version, 2.11.0b1-b4. b1 contained "Allow breaking configuration inheritance", b2 also [358](https://github.com/gitlabform/gitlabform/pull/358), b3 also a fix of a bug that caused breaking config inheritance to not work in some cases, b4 - [#361](https://github.com/gitlabform/gitlabform/issues/361)).

* Fix a problem causing some changes to not be applied. Fixes [334](https://github.com/gitlabform/gitlabform/issues/334). PR [#350](https://github.com/gitlabform/gitlabform/pull/350).

* **Deleting deploy keys is now possible**. This partially implements [193](https://github.com/gitlabform/gitlabform/issues/193). Also completely replace the implementation of deploy keys, secret variables and group secret variables with a new universal one. This possibly fixes [#19](https://github.com/gitlabform/gitlabform/issues/19).
* **Up to 40% faster thanks to making less requests to GitLab.** (For almost 1000 repositories the apply time has dropped from ~18 minutes to ~11 minutes.)
* With debug enabled a lot less duplication and a more readable output of dicts (shown as JSONs).
* **For Contributors** Introduce `SingleEntityProcessor` that generalizes editing things that are single per project, f.e. settings or push rules set. It does not edit entities if there are not changes to be applied. Using it implementing new features can be superfast! (See also `MultipleEntitiesProcessor` added in v2.2.0).
* **For Contributors** Faster tests and improved usage of fixtures.

(A pre-release of 2.9.2 RC1 contained some of the above changes. 2.10.0rc1 pre-release was the same as 2.10.0 final but with a slightly different changelog - the speed gains turned out to be higher than expected.)

* Fix version 2.9.0 not even starting. 🤦‍♂️ Add test to prevent this from happening again.

* **Access level names (not only their numbers) are now accepted in the configuration**.
* More strictness in parsing configuration YAML and better error messages thanks to a switch to different libraries. F.e. hash keys overwriting is not accepted anymore.
* Moved the project from `egnyte/gitlabform` to `gitlabform/gitlabform` and switch to GitHub Registry as the new main Docker registry.