Control the availability of developer mode on extensions page

Control if users can turn on Developer Mode on edge://extensions.

If the policy isn't set, users can turn on developer mode on the extension page unless DeveloperToolsAvailability policy is set to DeveloperToolsDisallowed (2).
If the policy is set to Allow (0), users can turn on developer mode on the extensions page.
If the policy is set to Disallow (1), users can't turn on developer mode on the extensions page.

If this policy is set, DeveloperToolsAvailability can no longer control extensions developer mode.

Policy options mapping:

* Allow (0) = Allow the usage of developer mode on extensions page

* Disallow (1) = Do not allow the usage of developer mode on extensions page

Use the preceding information when configuring this policy.