Backport: Add option to disable seperated caches

What does this MR do and why?

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As a fix for #330047 (closed), the caches of protected and non-protected branches were separated. This was a breaking change for customers (see #360910 (closed)). To fix the breaking change, a feature was added in #361643 (closed) to give customers the option of disabling the "cache separation".

Since #330047 (closed) was a security issue, the "cache separation" fix was backported to 14.10, 14.9 and 14.8. The option to turn off the breaking change (#361643 (closed)) was merged into 15.0, but many customers will not be able to upgrade to 15.0 for a long time due to 15.0 being a major release with a lot of breaking changes.

This MR backports !86876 (merged) into 14.10.3.

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