Docs: Update dashboard instructions for alert configs

[aeluce]

Description:

Updates docs to note new alert configuration options in the dashboard and specifies which functionality is available through the dashboard vs. flowctl on the customization page, which previously was solely focused on flowctl instructions.

Documentation links affected:

Pages on notifications and customizing alerts.

Notes for reviewers:

Thanks for reviewing! Updates are fairly minimal; open to further changes if needed, though the dashboard instructions feel pretty self-explanatory.

[github-actions]

🚀 Preview deployed to https://docs.estuary.dev/pr-preview/pr-3327/

📄 Changed pages:

• /guides/notifications/customize-alerts/
• /reference/notifications/

[jonwihl]

LGTM. There should be a note that you can't create duplicate alert subscriptions for the same prefix. Ex. There can only be one alert subscription for AcmeCo/ and you should edit the existing rules or add new alerts for prefixes instead

[jwhartley]

I have a customer asking for this doc so I'm going to merge it @aeluce , if you want to add the note Jonathan mentioned can you please do it in a new PR sorry

[jwhartley]

also @jonwihl task failure alert parameters aren't configurable in the UI yet?

[aeluce]

Data movement seems to be the only global setting currently and the UI PR didn't return hits when searching for task/shard failures. Would love to be proven wrong if you find otherwise.

[jonwihl]

Thats correct, task failure configuration isn't available yet