Fix admin users grid rendering and provider/source normalization

[CharlesGrimont]

Summary

This work fixes multiple issues in the admin users screens related to incomplete user data, provider display, source filtering, and UI consistency between the users list and the users-within-groups view.

What was fixed

• Fixed the users grid so rows no longer render empty when some user fields are missing.
• Added safe fallbacks for missing mail, language, and provider values.
• Fixed admin-side user creation so new users are created with provider = "forms".
• Added a backend fallback so missing providers default to forms.

Provider/source normalization

• azuread is displayed and filtered as Microsoft.
• ad is displayed and filtered as Active Directory.
• ad is displayed and filtered as LDAP when C8Oforms.useGenericLDAP == "true".
• forms or missing provider is displayed and filtered as No Code Studio.

Filter and UI updates

• Added a dedicated Active Directory / LDAP source filter.
• Kept Microsoft separate from Active Directory / LDAP.
• Replaced the old Convertigo label with No Code Studio everywhere in the admin grid and source filters for forms or empty providers.
• Updated the grid badges and source filters to use the same provider mapping rules on both admin screens.
• Improved provider badge contrast for better readability.
• Aligned the Contact column rendering consistently between the main admin users page and the users-within-groups page.

Backend support

• Exposed useGenericLDAP in the admin users endpoints so the UI can switch between Active Directory and LDAP consistently.

Expected result

• User rows display correctly even with partial data.
• Newly created admin users are consistently stored as Forms users.
• Source filters now match the intended provider semantics.
• The UI consistently shows Microsoft, Active Directory / LDAP, and No Code Studio with correct filtering and rendering behavior on both admin user screens.