Support "replacert" in overlays

**Describe the problem/challenge you have**

I would like to be able to, in one overlay operation:
- replace a {map item, array item, document} if it exists with my content; _or_
- append my content as a new item in the collection.

Today, I need to do that in two operations:
```
#@overlay/match by=overlay.subset({"kind":"Deployment", "metadata":{"name":"frontend"}})
---
spec:
template:
spec:
containers:
#@overlay/match by=overlay.subset({"name": "webserver"})
-
#@overlay/match missing_ok=True
#@overlay/remove
args:

#@overlay/match by=overlay.subset({"kind":"Deployment", "metadata":{"name":"frontend"}})
---
spec:
template:
spec:
containers:
#@overlay/match by=overlay.subset({"name": "webserver"})
-
#@overlay/match missing_ok=True
args: #@ data.values.deployment.args
```

**Describe the solution you'd like**

I'd rather `@overlay/replace` have an "replacert" behavior.

If that were the case, this would accomplish the same thing as above with just one overlay, greatly simplifying it:
```
#@overlay/match by=overlay.subset({"kind":"Deployment", "metadata":{"name":"frontend"}})
---
spec:
template:
spec:
containers:
#@overlay/match by=overlay.subset({"name": "webserver"})
-
#@overlay/match missing_ok=True
#@overlay/replace
args:
```

**Anything else you would like to add:**
The verbosity of doing this in multiple operations grows noticeably as the number of items being overlay'ed within the map increases