Merge branch 'kcj-add-philosophy' into 'master'

Adds PHILOSOPHY.md and references Product Handbook

See merge request gitlab-org/gitlab-ee!8515

PHILOSOPHY.md

+This document is intended to communicate the product philosophy GitLab uses in creating GitLab Enterprise Edition. The principles can be found in the [Product Section of the GitLab Handbook](https://about.gitlab.com/handbook/product/#product-at-gitlab).
\ No newline at end of file

ee/changelogs/unreleased/kcj-add-philosophy.yml

+---
+title: Adds PHILOSOPHY.md and references GitLab Product Handbook.
+merge_request: 8515
+author:
+type: other