Design and document a `Builder` pattern for API payloads

**Is your feature request related to a problem? Please describe.**
A real (incorrect) example of creating a card is something like this (not using the library, just `httpx` and ignore the hard coded URLs

```python
# Make a call to issue a card
add_payload = {
"cards": {
"add": [{
"type": {
"href": "https://commandcentre-api-au.security.gallagher.cloud/api/card_types/301"
},
"invitation": {
"singleFactorOnly": True
}
}]
}
}

# Use httpx to call cardholder.edit.href with this payload
async with httpx.AsyncClient() as client:
# add the header "Authorization: GGL-API-KEY"
client.headers["Authorization"] = "GGL-API-KEY " + os.environ.get("GACC_API_KEY")
response = await client.patch(str(cardholder.edit.href).replace("/edit", ""), json=add_payload)
```

The same payload can have a `"remove"` key with a card `href` which would make the command centre add a card and remove another in the same call.

To express this properly we should consider a builder pattern for the API payloads.

These make the Python code extremely expressive.

I have experienced similar things in Stripe's Terminal SDK where you want to conditionally add a payload.

**Describe the solution you'd like**
Consider providing a base `utility` class that payload builders can inherit from and it ultimately is able to produce the JSON that is sent to the server.

It could look something like:

```python
add_card_href = CardTypeRef(href="https://api.example.com/cards/123")
remove_card_href = HrefMixin(href="https://api.example.com/cards/456")

card_update_builder = CardholderUpdateBuilder()
.add_card(add_card_href)
.remove_card(remove_card_href)
.build()
```

This would allow conditional chaining of requests.

Some things to consider here are:
- Should we allow the user to pass `hrefs` or `ids` of particular objects (this is probably something I need to consider broadly around the project
- What does inheritance look like for payload providers

**Describe alternatives you've considered**
NA

**Additional context**
- [Builder pattern in Python](https://refactoring.guru/design-patterns/builder/python/example)