Don't add custom `AzureWebJobsStorage` emulator string if nothing changed

[MicroFish91]

We currently always intercept AzureWebJobsStorage emulator strings and replace it when setting up the environment vars for the func host start task. See background for this here: https://github.com/microsoft/vscode-azurefunctions/pull/4734#issue-3492723259

I think it's probably better if we don't always replace the string when it's an emulator, but only when it ends up actually deviating from the default. The reason for this is that it likely makes users uneasy when they see this message from the func CLI:

Skipping 'AzureWebJobsStorage' from local settings as it's already defined in current environment variables.

See similar explanation here: https://github.com/microsoft/vscode-azurefunctions/pull/4734#issuecomment-3378427434

[MicroFish91]

We may want to consider adding additional logging here as well.