Move to minimum role project create restriction

What does this MR do and why?

As group setting of Roles allowed to create projects means minimum roles allowed to create projects, I changed code like below.

• Added the word minimum to the dropdown title.
• Changed the dropdown item of Developers + Maintainers to Developers.
• Renamed DEVELOPER_MAINTAINER_PROJECT_ACCESS to DEVELOPER_PROJECT_ACCESS throughout the codebase, including variable and method names of a similar nature. (Because DEVELOPER_MAINTAINER_PROJECT_ACCESS meant Developers + Maintainers.)
• Added one test for user#manageable_groups after renamed the method's argument name. Because I found that there wasn't a test for it.
• Changed the order of the dropdown items from highest to lowest roles.

References

#507410 (closed)

MR acceptance checklist

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Screenshots or screen recordings

Please see the dropdown title, the item of Developers and the items' order.

• Group settings

Before	After

• Group settings in admin area

Before	After

• Default settings in admin area

Before	After

How to set up and validate locally

1. Open gdk in a browser, and log in as an admin user.
2. Open group settings. http://gdk.local:3000/groups/twitter/-/edit#js-permissions-settings
   See Minimum roles allowed to create projects. (Please read it differently, if your gdk's domain and group names are different)
3. Open group settings in admin area. http://gdk.local:3000/admin/groups/twitter/edit
   See Minimum roles allowed to create projects.
4. Open default settings in admin area. http://gdk.local:3000/admin/application_settings/general#js-visibility-settings
   See Default minimum roles for project creation protection.

Concern

I changed Roles allowed to create projects to Minimum roles allowed to create projects of the dropdown title in group settings. I think Roles allowed to create subgroups below it also means minimum roles. I suggest to add word minimum to it in another MR.

The reason why it means minimum is that Owner and Maintainer with ::Gitlab::Access::MAINTAINER_SUBGROUP_ACCESS can create subgroups according to the following code.

https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/policies/group_policy.rb#L330

rule { maintainer & maintainer_can_create_group }.enable :create_subgroup

https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/policies/group_policy.rb#L20

condition(:maintainer) { access_level >= GroupMember::MAINTAINER }

Note

I found Gitlab::Access.project_creation_options in https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/views/admin/application_settings/_project_creation_level.html.haml#L6.
But I don't think this file is called from anywhere. So there isn't a screenshot.

Related to #507410 (closed)