Post message to Slack when ingest completes successfully

[eecavanna]

In this branch, I updated the ingest CLI script so that, when it finishes a successful run, if a Slack incoming webhook URL is defined, the script uses that URL to post a message to a Slack channel. This technique for posting messages to Slack is documented here.

Outside of this PR, I have created a Slack app and—for that Slack app—generated an incoming webhook URL. That is what I plan to use on Spin (in all of our environments) once this code gets deployed there. For any reviewers that intend to test this locally, I can also provide that URL to you via Snappass (or Spin). Using that specific URL, the Slack message will be posted to the newly-created #ingest-notifications channel in the NMDC Slack workspace.

[eecavanna]

Thanks for reviewing/approving this.

Spin/Rancher has been configured with the Slack incoming webhook URL

Before merging this branch in, I have added the Slack incoming webhook URL to Rancher.

Specifically, in both the development and production environments (i.e. nmdc-dev and nmdc namespaces): I created an opaque secret named slack, which has an item whose key is SLACK_WEBHOOK_URL_FOR_INGESTERand whose value is that Slack incoming webhook URL. Then, I configured the portal-ingest CronJob so that it has an environment variable named SLACK_WEBHOOK_URL_FOR_INGESTER whose value comes from that secret key (as shown in the following screenshot).

As a result, once this gets merged into main, the next time the ingest runs successfully in the development environment, I expect a message to appear in the #ingest-notifications Slack channel.

In addition, after the next monthly NMDC release (i.e. when this code gets deployed to production), I expect a message to appear in that Slack channel whenever ingest runs successfully in production.