get https://{tenanturl}/v1.0/branding/themes
List all the themes that are registered for the tenant.
Generates a list of registered themes for the tenant, which includes theme name and description(optional).
Default theme is always present since it is the current themeID for your Verify tenant.
Entitlements required:
manageTemplates (Manage templates and themes) or readTemplates (Read templates and themes)