This commit holds WIP for the peadm::restore plan.

This commit refactors the restore plan for style (line folding, variable
names, etc) and flow, mainly an attempt to find a single path that
always works, and eliminate conditional logic.

The plan is not yet validated at this stage. More work is required to
ensure correct functionality.

WIP: doing testing/validation and fixing logic

Because the PuppetDB database exists separately on two PostgreSQL hosts
in a DR configuration, adapt the restore plan to restore the data to
BOTH locations, if they exist

Specifically, make it handle situations where PuppetDB queries return
multiple results for server() queries, which could happen in the event a
database has been backed up on one cluster, and restored into another.

Note what additional action needs to take place when there is dev time

This should help keep current cluster PuppetDB knowledge of cluster
hosts after restoring PuppetDB data from a backup

They aren't ready yet for full use

(SOLARCH-581) Implement restore plan

…grade docs

…ture-link-to-install-doc

Fix docs references from "provision" to "install"

Adds support for the newly released versions

This will let users specify the download URL to retrieve the PE tarball
from.

Support PE 2021.6 and 2019.8.11

To permit upgrades to download installer media from arbitrary URL

Update parameters a little bit. They still aren't totally right but this
is a minor improvement.

Add optional `pe_installer_source` parameter

Release prep v3.7.0