Adding manage roles page to docs (#603)

* Adding manage roles page to docs

* Adding instructions for assigning principals and grants to a role

* adding terraform to assign principles example and assign grants example

* docs: add role clickthroughs and step-by-step instructions

* Removing old manage role screenshots for admin workflow

Co-authored-by: Pete Pacent <ppacent@hashicorp.com>
Co-authored-by: Randall Morey <randall@randallmorey.com>

website/data/docs-navigation.js

@@ -86,6 +86,7 @@ export default [
       'manage-scopes',
       'manage-targets',
       'manage-identities',
+      'manage-roles',
       'manage-sessions',
     ],
   },