chore: rename manager/member to administrator (#11542)

# Which Problems Are Solved

As part of the naming consistency initiative, the terms `Manager`,
`Member` and other similar terms that are used in the context of an
administrator are replaced by `Administrator` in the UI and
documentation.

# How the Problems Are Solved

By replacing the following terms with Administrator / Administrator
Roles in docs, Console UI, and guides.

- Manager
- Add Manager
- Add a Manager
- Administrator (used as a person type)
- Membership
- Member grants

# Additional Changes
minor grammatical edits in the docs

# Additional Context
- Closes https://github.com/zitadel/zitadel/issues/11291

---------

Co-authored-by: Marco A. <[email protected]>

apps/docs/lib/sidebar-data.ts

@@ -47,7 +47,7 @@ export const guidesSidebar: readonly SidebarItem[] = [
           "guides/manage/console/projects-overview",
           "guides/manage/console/applications-overview",
           "guides/manage/console/users-overview",
-          "concepts/structure/managers",
+          "concepts/structure/administrators",
         ],
       },
       {
@@ -679,7 +679,7 @@ export const guidesSidebar: readonly SidebarItem[] = [
           "guides/manage/console/roles",
           "guides/integrate/retrieve-user-roles",
           "concepts/structure/granted_projects",
-          "guides/manage/console/managers",
+          "guides/manage/console/administrators",
         ],
       },
       {