feat(staging): inbound links so /odoo-staging-environment/ is not an orphan

The copy's 'Into this page' table, applied as single additive sentences:
- support.html: the 'error 500 after a git check in' FAQ answer links
  'test it safely first'.
- blog/posts/speed-run-backup.html: end of the post links
  'what a staging environment is, and why you probably do not need one'.
- odoo-hosting-2027.html: one contextual note by the backup/module rows
  links 'do you need a staging environment?'.
- index.html: one FAQ card 'Do you need an Odoo staging environment?'.
No footer change. No new impeccable finding category.

odoo-hosting-2027.html

@@ -754,6 +754,15 @@
               panel. It is optional. The business works exactly the same without it.
             </p>
           </div>
+          <div class="cmp-note">
+            <h3>Do you need staging?</h3>
+            <p>
+              A staging environment is a second copy of your system you are allowed to break. It is the right
+              tool when you change Odoo's code, and overkill when you install a finished module on a backup.
+              We wrote out <a href="/odoo-staging-environment/">do you need a staging environment?</a>, and the
+              simpler route we recommend first.
+            </p>
+          </div>
         </div>
       </div>
     </section>