added matomo upgrade instructions

[joshdentremont]

Added instructions on how to recreate the matomo volume in order to update to a new version of Matomo

Purpose / why

Upgrading from buildkit 1.x to 2.x requires updating matomo

What changes were made?

instructions added

Verification

1. Create a site using TAG 1.0.10
2. Set Matomo to track site visits so that you get some data in your Matomo database
3. upgrade to TAG 2.0.10
4. Follow these instructions to update Matomo to 4.15.1
5. Check that site data is still available and that new site visits are tracked

Interested Parties

Islandora-Devops/isle-dc#356

• @Islandora/documentation
• @Islandora/committers

Checklist

Pull-request Reviewer

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

The 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?

[joshdentremont]

These instructions may cause a loss of installed plugins, as possibly other customizations. I think more investigation is required.

Looks like the recommended way is to update through the web UI, so maybe we should document that instead.
matomo-org/docker#248