TCLOUD-4894: add stale-if-error cache-control header

[tiny-mcg]

Ticket: TCLOUD-4894

Site: Staging branch

Changes:

• Adds stale-if-error to serve a stale response when errors occur with the proxy.

Pre-checks:

• Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.
• modules/ROOT/nav.adoc has been updated (if applicable).
• Included a release note entry for any New product features.
• If this is a minor release, updated productminorversion in antora.yml and added new supported versions entry in modules/ROOT/partials/misc/supported-versions.adoc.

Review:

• Documentation Team Lead has reviewed