Text updates: saltstack/saltstack-remediation

Includes minor text revision in README, as well as these documented in the changelog:

Update display_name to SaltStack Remediation (from SaltStack) to match GitHub
Remove none option for API username and password in integration yaml
Revise text labels and prompts in configuration modal
Add pipeline reference setup step and example in README
List and describe options for sensu.io/plugins/sensu-saltstack-handler/config/actions annotation in README
Update README link references to match headings on the linked pages
Revise list of reference documentation in README

sensu / catalog