fix(ui): turn off GKE metadata by default

[gregsheremeta]

Description of your changes:

Since GKE is only one of many platforms, change the default value of DISABLE_GKE_METADATA to true. Edit the gcp manifest to override that to false on GCP.

Fixes: #11247

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[google-oss-prow]

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[HumairAK]

the frontend failures here are relevant:

Details

 FAIL ./app.test.ts
  ● Console

    console.log integration-tests/test-helper.ts:1867
      beforeAll, writing files
    console.info node_modules/http-proxy-middleware/lib/logger.js:81
      [HPM] Proxy created: /  ->  http://localhost:9090

  ● UIServer apis › /system › /cluster-name › responds with cluster name data from gke metadata

    expected 200 "OK", got 500 "Internal Server Error"

      at Test._assertStatus (node_modules/supertest/lib/test.js:268:12)
      at Test._assertFunction (node_modules/supertest/lib/test.js:283:11)
      at Test.assert (node_modules/supertest/lib/test.js:173:18)
      at localAssert (node_modules/supertest/lib/test.js:131:12)
      at node_modules/supertest/lib/test.js:128:5
      at Test.Request.callback (node_modules/superagent/lib/node/index.js:728:3)
      at IncomingMessage.<anonymous> (node_modules/superagent/lib/node/index.js:916:18)

  ● UIServer apis › /system › /cluster-name › responds with 500 status code if corresponding endpoint is not ok

    expected 'Failed fetching GKE cluster name' response body, got 'GKE metadata endpoints are disabled.'

      at error (node_modules/supertest/lib/test.js:301:13)
      at Test._assertBody (node_modules/supertest/lib/test.js:218:14)
      at Test._assertFunction (node_modules/supertest/lib/test.js:283:11)
      at Test.assert (node_modules/supertest/lib/test.js:173:18)
      at localAssert (node_modules/supertest/lib/test.js:131:12)
      at node_modules/supertest/lib/test.js:128:5
      at Test.Request.callback (node_modules/superagent/lib/node/index.js:728:3)
      at IncomingMessage.<anonymous> (node_modules/superagent/lib/node/index.js:916:18)

  ● UIServer apis › /system › /project-id › responds with project id data from gke metadata

    expected 200 "OK", got 500 "Internal Server Error"

      at Test._assertStatus (node_modules/supertest/lib/test.js:268:12)
      at Test._assertFunction (node_modules/supertest/lib/test.js:283:11)
      at Test.assert (node_modules/supertest/lib/test.js:173:18)
      at localAssert (node_modules/supertest/lib/test.js:131:12)
      at node_modules/supertest/lib/test.js:128:5
      at Test.Request.callback (node_modules/superagent/lib/node/index.js:728:3)
      at IncomingMessage.<anonymous> (node_modules/superagent/lib/node/index.js:916:18)

  ● UIServer apis › /system › /project-id › responds with 500 status code if metadata request is not ok

    expected 'Failed fetching GKE project id' response body, got 'GKE metadata endpoints are disabled.'

      at error (node_modules/supertest/lib/test.js:301:13)
      at Test._assertBody (node_modules/supertest/lib/test.js:218:14)
      at Test._assertFunction (node_modules/supertest/lib/test.js:283:11)
      at Test.assert (node_modules/supertest/lib/test.js:173:18)
      at localAssert (node_modules/supertest/lib/test.js:131:12)
      at node_modules/supertest/lib/test.js:128:5
      at Test.Request.callback (node_modules/superagent/lib/node/index.js:728:3)
      at IncomingMessage.<anonymous> (node_modules/superagent/lib/node/index.js:916:18)

so we'd need to address those somehow