fix: change static legend's hide property to show

[TCL735]

In support of influxdata/ui#1666

On the backend, static legend's properties must always be tracked. For hide there are really 3 states: true, false, or not set.

This is different than on the frontend, where Giraffe sees a lack of a "static legend" object to mean that static legend is not desired. And static legend's hide property is for convenience; it is a way to temporarily hide the static legend without removing (and later rebuilding) the entire object. Thus it is the static legend object itself that is analogous to the backend's hide property -- and has 3 states: staticLegend.hide is true, staticLegend.hide is false, or the lack of staticLegend.

Thus, on the backend we should change hide to show to accurately reflect "not set" to be the same as false.

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (if modified Go structs or API)
• Feature flagged (if modified API)
• Documentation updated or issue created (provide link to issue/pr)
• Signed CLA (if not already signed)

[williamhbaker]

LGTM, thanks for the PR & for the detailed explanation!