Validate: add ability to check if code insights works on an instance

[mucles]

context: https://sourcegraph.slack.com/archives/C022SPMNR0W/p1672950729445719
Implementation Engineer will use script to verify if instance is configured correctly and can create basic code insights and batch changes

Test plan

locally tested using the scale test instance to create an insight
created yaml file

createInsight:
  title: "Javascript to Typescript migration" 
  dataSeries:
    [ {
        "query": "lang:javascript",
        "label": "javascript",
        "repositoryScope": [
            "github.com/sourcegraph/sourcegraph"
          ],
        "lineColor": "#6495ED",
        "timeScopeUnit": "MONTH",
        "timeScopeValue": 1
      },
     {
        "query": "lang:typescript",
        "label": "typescript",
        "lineColor": "#DE3163",
        "repositoryScope": [
            "github.com/sourcegraph/sourcegraph"
          ],
        "timeScopeUnit": "MONTH",
        "timeScopeValue": 1
      }
    ]

ran go run ./cmd/src validate validate.yaml

[leonore]

hey, I'm not familiar with usage of src validate, but be aware if this is ran against an actual instance the code insight will live there and continuously backfill if you don't clean up- don't know if that might get confusing? just thought I'd comment :)

edit- this is how we clean up in our integration tests if you wanted to clean up after validation: https://sourcegraph.sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/dev/gqltest/code_insights_test.go?L252-256