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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[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. (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. (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. (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. (node_modules/superagent/lib/node/index.js:916:18) ```

so we'd need to address those somehow