Core/Ent: Add `/health` endpoint example to upgrade

[jstirnaman]

Add /health endpoint example for checking status

Not related to this PR but I feel it would be useful to have a infludb3 health command to forward to the /health API for cases like this.

Originally posted by @hiltontj in #6483 (comment)

[hiltontj]

Just to clarify - A influxdb3 health command does not yet exist. We'll need to add that.