As a LU, I want to configure group types and group visibility for fleixble groups to allow for more customization

Problem/Motivation

We plan to provide only flexible groups in future.
However to do this, we need to make Flexible groups easier to configure and more extendable.
Currently, the configuration interface for flexible groups is
1) overwhelmed with all the options
2) missing the option to configure the group visibility. - https://github.com/goalgorilla/open_social/pull/2076
3) missing a group type field to categorize what kind of group it is (local, closed, secret, event based you name it). - https://github.com/goalgorilla/open_social/pull/2140

Proposed resolution

We will improve the flexible group type with:

1/2) A new group visibility field. This field is used to differentiate to whom the Group is shown in the overviews and search, so in essence who can find a group.
We will make sure the existing fields are better explained, and less options occur with better explanatory texts.

See attached screenshots for the new Group configuration for flexible groups.

3) We will add a new group type vocabulary. Add a new field group type to the flexible groups, and a setting to the Group settings within Open Social. By enabling the setting and adding group types you are now able to categorize your flexible groups.
This adds extra informative and categorize options, which will increase in value when we have flexible groups as only available option in Open Social.