POST request to install an already installed snap yields misleading error message

[Bill Kronholm]

Making a POST request to the Snapd REST API to install a snap that is already installed yields a message saying there are no results from the store.

# snap install hello-world
hello-world 6.4 from Canonical✓ installed
# sudo curl -sS --unix-socket /run/snapd.socket http://localhost/v2/snaps -X POST -H 'Content-Type: application/json' -d '{"action": "install", "snaps": ["hello-world"]}' | jq
{
  "type": "error",
  "status-code": 400,
  "status": "Bad Request",
  "result": {
    "message": "cannot install \"hello-world\": no install/refresh information results from the store"
  }
}

It's probably better to return the same response as from snap:

# snap install hello-world
snap "hello-world" is already installed, see 'snap help refresh'

This issue may be related to this bug report: https://bugs.launchpad.net/snapd/+bug/1843725