Update the website to use Hugo's alias feature for stable redirects

[aj-stein-gsa]

Update the website to use Hugo's alias feature to support more stable URLs and targeted documentation shifts with targets to the actual docs (https://automate.fedramp.gov/help/constraint/frr987 redirects to https://automate.fedramp.gov/documentation/ssp/5-attachments/#system-inventory-approach as an example).

To make the task clear and ready to work for staff who pick it up, I set up this repo with the templates and two examples to churn through the rest at https://github.com/GSA/automate.fedramp.gov_private/pull/68.