[CLI]: Verb/Option for configuring "behavioral" feature flags (`--enable-feature-123`)

To track as a separate issue, I think we should add a different `dab` command that helps to enable or disable a feature, should not be only possible through the `init` command - which is the case today.

_Originally posted by @Aniruddh25 in https://github.com/Azure/data-api-builder/pull/1983#discussion_r1468255119_

Create a new command to create/update feature flags in the config file.

Start by examining the existing `dab` CLI and its `init` command, then trace how feature flags are written to the config file. Define the command's enable and disable behavior and verify that it can create or update the relevant configuration entries without requiring `init`.

Written by the indexing model from the issue text.