Remove support for AzureWebJobsDashboard

[brettsam]

Discussion: https://github.com/Azure/Azure-Functions/discussions/1925

Remove support for the WebJobs dashboard.

Motivation

The dashboard has been in an "unsupported" mode for v3, but still works. We'd like to completely remove support to make it clear that this is not something we're maintaining.

Impact

Not entirely sure -- this has been disabled during site creation for a while but is likely enabled on a large number of sites. I can't find any metric or log that we emit that tells us that the dashboard is enabled, so to gather the numbers we may have to emit a metric or log message. This may be worthwhile no matter what for the "migration guide" detector that we've discussed.

Compat-mode support

None. We have no support for this going forward.

Alternatives

App Insights, Log Analytics.

Detection

We can emit a warning if the AzureWebJobsDashboard is present.

Support

I don't believe so.

Documentation

This topic will need updating: https://docs.microsoft.com/en-us/azure/azure-functions/functions-app-settings#azurewebjobsdashboard

Components impacted

This affects:

• Host. We'll need to update the FunctionInstanceLogger to ignore the Dashboard setting.

All app creation flows already leave this off.

Performance

We recommend against using the dashboard today, but this will force it. Some customers may see a perf improvement now that it would be removed completely.

[brettsam]

Follow-up work items:

• Emitting a log statement AzureWebJobsDashboard is configured azure-functions-host#7447
• Remove AzureWebJobsDashboard support in v4 azure-functions-host#7647