ACME External Account Binding Support (#2096)

[rosiel]

Adds documentation on configuring Traefik for External Account Binding with ACME.

Replaces #2096 which was merged too early.

Purpose / why

Update Docs for ACME External Account Binding.

This can't be merged until Islandora-Devops/isle-dc#253 is merged, otherwise the feature doesn't exist.

What changes were made?

Add documentation for how to configure External Account Binding with ACME

Verification

Utilize an SSL Certificate provide that supports External Account Binding to request SSL Certificate. Verify you get SSL certificate from your provider, and not Let's Encrypt. A couple of options include InCommon and ZeroSSL.com

Interested Parties

@Islandora/documentation

---

Checklist

Pull-request reviewer should ensure the following

• Does this PR link to related issues?
• Does the proposed documentation align with the Islandora Documentation Style Guide?
• Are the changes accurate, useful, free of typos, etc?

Person merging should ensure the following

• Does mkdocs still build successfully? (This is indicated by TravisCI passing. To test locally, and see warnings, see How To Build Documentation.)
• If pages are renamed or removed, have all internal links to those pages been fixed?
• If pages are added, have they been linked to or placed in the menu?
• Did the PR receive at least one approval from a committer, and all issues raised have been addressed?

Related Tickets

Islandora-Devops/isle-dc#253
Islandora-Devops/isle-dc#252
#2096

[misilot]

@rosiel this should be good now. Islandora-Devops/isle-dc#253 just got merged