Make improvements to features.yml to enable better price tier decisions

Problem Statement: We have hundreds of paid features. We need better data about each feature to make more informed price tier decisions.

One challenge is presenting our features on our pricing page in a way that best communicates the value of each GitLab tier in a differentiated manner. To do that, we are leveraging "themes" on the pricing page. This document captures the themes that we're currently testing on our pricing page: https://docs.google.com/document/d/1EOc_9lFbxh9UaY3TcB0fo9FIiN9KtePGlk8rWK3w9O8/edit. I suggest we add a field called "Theme" in features.yml, and if a given feature rolls up to a pricing page theme we can capture that in features.yml. From there, we could automate the pricing page to ensure that it's pulling in all features related to that theme.

A second challenge is that we have some data on purchase intent from the Post Purchase Survey (https://about.gitlab.com/direction/product-operations/#post-purchase), but that data is not leveraged well in other areas yet. I suggest we add a field to features.yml called "Purchase Driver" and populate integer scores from the most recent post purchase survey.

Then we can identify paid features that aren't a purchase driver, and aren't related to pricing page themes, and those could be prime candidates for registration features or open sourcing.