fix(chart/backups): normalize S3 endpoint scheme — close CN parity Bug #4 (Slice 12.4)

awscli --endpoint-url rejects bare hostnames ("scheme is missing").
Tower's migrate path emitted bare s3-cn-gd.ufileos.com for CN
tenants, which booted every scheduled backup pod into Error within
seconds. Chart-side fix: prepend https:// when missing, resilient
to either shape. Bumped 0.1.12 -> 0.1.13.

Render-tested both shapes:
  endpoint: s3-cn-gd.ufileos.com    -> "https://s3-cn-gd.ufileos.com"
  endpoint: https://s3.amazonaws.com -> "https://s3.amazonaws.com"

Chart.yaml

@@ -5,7 +5,7 @@ description: |
   Variation between instances is expressed via values.yaml only.
   No chart variants. No string-templating in Tower.
 type: application
-version: 0.1.12
+version: 0.1.13
 appVersion: "1.0"
 keywords:
   - odoo