Allow merging list policies from different sources

Setting the policy allows merging of selected policies when they come from different sources, with the same scopes and level.

Use the wildcard character '*' to allow merging of all list policies.

If a policy is in the list and there's conflict between sources with:

* The same scopes and level: The values merge into a new policy list.

* Different scopes or level: The policy with the highest priority applies.

If a policy isn't in the list and there's conflict between sources, scopes, or level, the policy with the highest priority applies.

Example value:

ExtensionInstallAllowlist
ExtensionInstallBlocklist