feat: support client verify for derp (add integration tests) (#2046)

* feat: support client verify for derp

* docs: fix doc for integration test

* tests: add integration test for DERP verify endpoint

* tests: use `tailcfg.DERPMap` instead of `[]byte`

* refactor: introduce func `ContainsNodeKey`

* tests(dsic): use string builder for cmd args

* ci: fix tests order

* tests: fix derper failure

* chore: cleanup

* tests(verify-client): perfer to use `CreateHeadscaleEnv`

* refactor(verify-client): simplify error handling

* tests: fix `TestDERPVerifyEndpoint`

* refactor: make `doVerify` a seperated func

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Co-authored-by: 117503445 <t117503445@gmail.com>

.github/workflows/test-integration.yaml

@@ -38,6 +38,7 @@ jobs:
           - TestNodeMoveCommand
           - TestPolicyCommand
           - TestPolicyBrokenConfigCommand
+          - TestDERPVerifyEndpoint
           - TestResolveMagicDNS
           - TestValidateResolvConf
           - TestDERPServerScenario