Return false for integration.IsEnabled if key unset in replicated secret

[dexhorthy]

What this PR does / why we need it:

The logic here appears to be flipped - if the integration key is absent or empty, I would guess that means "false"

Steps to reproduce

• Do any standard SDK install (i.e. not in integration mode)
• curl the /api/v1/app/info endpoint via your desired route (exec, port-forward, etc)
• receive mock data with incorrect helmChartURL and currentRelease

{
  "appSlug": "slackernews-dexter-s-version",
  "appName": "SlackerNews (Dexter's Version)",
  "appStatus": "ready",
  "helmChartURL": "oci://registry.replicated.com/dev-app/dev-channel/dev-parent-chart",
  "currentRelease": {
    "versionLabel": "0.1.3",
    "releaseNotes": "release notes 0.1.3",
    "createdAt": "2023-05-23T20:58:07Z",
    "deployedAt": "2023-05-23T21:58:07Z",
    "helmReleaseName": "dev-parent-chart",
    "helmReleaseRevision": 3,
    "helmReleaseNamespace": "default"
  }
}

Does this PR introduce a user-facing change?

Fix a bug in the evaluation of "integration mode" for `/api/v1/app/info` and other related endpoints

Does this PR require documentation?

No, bug fix