Azure front door CLI is hard to integrate due to incremental changes

### Extension name (the extension in question)
front-door

### Description of issue (in as much detail as possible)

We are using the Azure CLI to control our front door configuration, but there are a lot of edge cases that are hard to implement due to that each incremental step has to be perfectly valid (the UI allows adjusting the state, then clicking "Save" to commit). Since every aspect of the front door configuration is its own command (unlike most other resources where a single command line can do everything), this turns out to be difficult to use.
For example, say that we want to replace all backends in a backend pool. One cannot simply delete the old ones and insert the new, since that would become an invalid configuration (a backend pool cannot be empty). But one cannot always create the new ones, since the backends will sometimes conflict with the old ones. This makes it very hard to update from a script.