Add a terminal attribute to request hash policy.
Think about a case where customers want to hash on a cookie if it's present but if it's not present, do best-effort sticky based on something like IP so the customer has a stable hash.
This "terminal" allows request hashing to have the ability of "if A not working, fallback to B.", which also saves time to generate the hash.
Changes:
* Add a terminal attribute to HashMethod, which shortcircuit the hash generating process if a policy is marked terminal and there is a hash computed already.
Signed-off-by: Xin Zhuang stevenzzz@google.com
Description: Add terminal attribute to request hash.
Risk Level: Low
Testing: unit tests.
Mirrored from https://github.com/envoyproxy/envoy @ ee710d0a92b476cc3d7a0f99f11b62675d1a4e01