Fix TOC structure: merge Quickstarts and How-to guides into Get started

Merge the separate Quickstarts and How-to guides sections back into a
single Get started section with 6 items to satisfy the 3-12 items per
section guideline. Preserves improved article names and ordering.

Co-authored-by: Copilot <[email protected]>

Author: kenieva

articles/governance/service-groups/toc.yml

@@ -2,7 +2,7 @@
   href: index.yml
 - name: What are Azure Service Groups?
   href: overview.md
-- name: Quickstarts
+- name: Get started
   items:
   - name: Create a service group in Azure portal
     href: create-service-group-portal.md
@@ -12,8 +12,6 @@
     href: create-service-group-member-portal.md
   - name: Add service group members with REST API
     href: create-service-group-member-rest-api.md
-- name: How-to guides
-  items:
   - name: Manage service groups and members
     href: manage-service-groups.md
   - name: Manage membership at scale