"functionapp publish" should export ConnectionStrings as well as AppSettings

Using `func functionapp publish` you can publish your local AppSettings (local.settings.json) to the remote instance of the app running in the Azure cloud.

At the moment there no way to publish ConnectionStrings (also contained into local.settings.json) to the remote instance.

The action `functionapp publish` should mirror `functionapp fetch-app-settings` behavior, where we get ConnectionStrings (other than AppSettings) imported from remote to local env.

Start by locating the `functionapp publish` and `functionapp fetch-app-settings` command entry points and the handling of `local.settings.json`. Compare how AppSettings and ConnectionStrings are transferred. Done means publishing also transfers ConnectionStrings to the remote Azure Function App, consistently with fetch-app-settings behavior.

Written by the indexing model from the issue text.