ClientSettingsPolicy for Gateways

[kate-osborn]

As a Cluster Operator
I want to set defaults for client settings that will work for most applications
so that most Application Developers will not have to tweak these settings.

Acceptance

• A user can create a ClientSettingsPolicy and attach it to a Gateway.
• The Accepted Condition is set on every ClientSettingsPolicy using the reasons defined in the PolicyCondition API. If these reasons are not sufficient, we can add implementation-specific reasons.

[mpstefan]

The completion of this issue will complete the work first defined in:

#1245