[L&R] Update L&R Onboarding module

Working on a few changes in the L&R module. Any and all feedback or participation is appreciated 🙏

Changes made:

1. Removed requirement to work on EULA Internal Requests. Marked EULA Basics as Optional.
2. Removed LicenseApp under Systems & Tools.
3. Moved Billable Members tasks to be under
4. Changed requirement to work on Billable Members from Internal Requests to ZD tickets.
5. Updated instructions about being added to licensing-subscription group to point to Slack group Access Request page.
6. Added Zuora walkthrough video.
7. Added Cloud Licensing Page.
8. Added requirement to work on 2 SM Trial Extension Internal Requests.
9. Added Activate Trial Runners Requests and Resend/Forward License Requests as part of Internal Requests

Pending:

1. Add more context regarding Activate Trial Runners Requests
2. Add more context and tasks to complete regarding Resend/Forward License Requests
3. Add instructions on how to join Internal Requests Hawk

Please feel free to add or make any more changes. Thanks!

/cc @rotanak @shemgyll @dserafin-gitlab @kevenhughes @mdunninger @rspainhower

/cc @gitlab-com/support/licensing-subscription