Epic (reporting): v2 release

In the v1 release, we added some summary metrics to the top of the features page (see screenshot below). In v2, we'd like to expand upon this to create a complete dashboard experience.

The data should be captured at regular intervals to allow us to track the data over time. This will mean capturing and storing the metrics implemented as part of v1 as well.

On top of the metrics currently displayed as part of v1, we'd like to add the following metrics:

Metric | Description
--|--
num of projects|
num of users|
number of environments|
num of features created|This metric will need to be evaluated over a given time period
num features deleted|This metric will need to be evaluated over a given time period
num features updated(requires versioning)|This metric will need to be evaluated over a given time period
num stale features (requires versioning)|
number of CR committed|This metric will need to be evaluated over a given time period
num segments|
num of identity overrides|
Average feature time from creation to use in a production environment|
Unused feature flags|i.e. usage is 0 for x days, this could help identify features that aren't actually being used

The dashboard should be filterable based on the following options:

- Time period
- Project
- Environment
- Tag
- Assigned user / group