Add Leaflet maxZoom to configParameters

[glughi]

What this PR does

Related to #7280

Add "leafletMaxZoom" to configParameters so that the maxZoom of the Leaflet viewer can be changed.

Test me

How should reviewers test this? (Hint: If you want to provide a test catalog item, create a Gist of its catalog JSON, add its url and your branch name to this url: http://ci.terria.io/<branch name>/#clean&<raw url of your gist> , and then paste that in the body of this PR)

Checklist

• [ ] There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• [ ] I've updated relevant documentation in doc/.
• [x] I've updated CHANGES.md with what I changed.
• [ ] I've provided instructions in the PR description on how to test this PR.

[CLAassistant]

All committers have signed the CLA.