Track usage data for Network Policies UI

What does this MR do?

Uses a redis HLL counter to track the number of clusters visiting the network policies page with network policies present in the cluster. Since any ultimate customer can visit the page, we require policies to be present in the response as an extra signal for the feature having provided value to the user.

Note: I did not add a feature flag because the number of users is expected to be low (internal link), so I don't think it would be worth the overhead.

See #334090 (closed)

Video

Demonstrates the page loading and the counter changing as a result:

2021-06-23_16-33-43

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.