Improve Cloud Starter - New Relic config instructions (#6809)

* Per PR #6708 - Improve instructions for configuring Starter projects
for New Relic reporting
-  Add prerequisites for credentials and role access required to add
the license key to an environment
-  Link to alternative instructions for getting the New Relic license
key from New Relic account, and adding the license key from the Magento
Admin
-  Added separate H3 headings for Configure Starter for New Relic and
Remove license key from Starter to make content easier to scan

* Clean up link references

- Changed all anchor reference links to inline links
- Alphabetized link reference list
- Removed numeric references

Co-authored-by: hguthrie <[email protected]>

Author: meker12