Add platform filter to Policies page, API, and fleetctl

[dherder]

Goal

User story
As a Fleet user,
I want to filter policies on the Policies page
so that I can remove my platform prefixes ("macOS -") from the policy names.

For help creating a user story, see "Writing a good user story" in the website handbook.

Change

• Add Targeted platforms column and platform filter to Policies page #44125

[noahtalerman]

Problem

When implementing many hundreds of policies, it is difficult to search for the exact policy that is needed. A search field and platform filter would be helpful.

Potential solutions

Show the same search field and platform filter as displayed in Queries page.

[allenhouchins]

Related: #44125

[allenhouchins]

Re-added :product label to discuss.