Shielding VCL Rendering, New VCL Syntax

vclchanged

Backend definitions with shielding enabled, and which use the 'shield' director, now have a simplified syntax that incorporates health checks, loop checks, and other checks in a single line of VCL.

Additionally, the minimum version of VCL available across our network increased, unlocking the following changes:

New variable

New function

Prior change: Remove beta tags from the Secret Store docs

Following change: Added percentage-based alerts