validate command

Created by: uwedeportivo

Adds a new validate command to src-cli. This command validates a Sourcegraph instance by executing a script given as an argument. The intention is to provide a way for admins of Sourcegraph instances to verify that their new install or their upgrade went well and the instance is functioning.

The validation steps are specified in a json structure. The validation follows this outline:

• create the first admin user
• use their credentials to create an external service
• wait for repo to clone
• execute a search and check the count on the result
• delete the external service

The spec is something like this (if some of the spec structs are not declared, then the corresponding step is skipped)

{
  "firstAdmin": {
    "email": "[email protected]",
    "username": "e2e-test-user",
    "password": "123123123-e2e-test"
  },
  "externalService": {
    "config": {
      "url": "https://github.com",
      "token": "{{ .github_token }}",
      "orgs": [],
      "repos": [
        "sourcegraph-testing/zap"
      ]
    },
    "kind": "GITHUB",
    "displayName": "footest",
    "deleteWhenDone": true
  },
  "waitRepoCloned": {
    "repo": "github.com/sourcegraph-testing/zap",
    "maxTries": 5,
    "sleepBetweenTriesSeconds": 2
  },
  "searchQuery": "repo:^github.com/sourcegraph-testing/zap$ SugaredLogger count:99999"
}

documentation for the command is here https://github.com/sourcegraph/sourcegraph/pull/12001