Validate: add deleteWhenDone option to insights

[jdpleiness]

Insights were automatically deleted, add option to keep insight created during validation via deleteWhenDone:

externalService:
  kind: GITHUB
  displayName: srcgraph-test
  deleteWhenDone: true
  maxRetries: 5
  retryTimeoutSeconds: 5
  config:
    gitHub:
      url: https://github.com
      orgs: []
      repos:
        - sourcegraph-testing/zap

searchQuery:
  - repo:^github.com/sourcegraph-testing/zap$ test
  - repo:^github.com/sourcegraph-testing/zap$@v1.14.1 test

insight:
  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
      }
    ]
  deleteWhenDone: true

Test plan

Locally tested changes using latest Sourcegraph Helm install. Tested default configuration if no YAML is provided, YAML configuration provided, and JSON configuration provided.

ran go test ./... - all tests passing
ran staticcheck ./... - no issues found in new code

[mucles]

Nice, this looks good to me 👍