feat: support enum object types

### Clear and concise description of the problem

I have the following type/model definitions:

```typescript
NonEmptyString:
type: string
minLength: 1
pattern: ^\S(?:.*\S)?$

PickValue:
type: object
properties:
text:
$ref: "#/$defs/NonEmptyString"
value:
type: integer
required:
- text
- value
```

I want to derive a type from `PickValue` so that only specific combinations of `text` and `value` values are valid. In a plain JSON Schema I'd create the following definition

```yaml
PartnerRole:
allOf:
- $ref: "#/$defs/PickValue"
- type: object
enum:
- text: "Insurance holder"
value: 805190000
- text: "Facilitator"
value: 805190001
- text: "Tenant"
value: 805190002
- text: "Insurer"
value: 805190003
- text: "Broker"
value: 805190004
- text: "other"
value: 805190008
required:
- text
- value
additionalProperties: false
```

Currently there is no way to express this in TypeSpec. Or I didn't find the right documentation yet.

The only way I found was to specify enum values for each property separately.

```typescript
model PartnerRole extends PickValue {
/*
Insurance holder 805190000
Facilitator 805190001
Tenant 805190002
Insurer 805190003
Broker 805190004
other 805190008
*/

@oneOf
text:
"Insurance holder" |
"Facilitator" |
"Tenant" |
"Insurer" |
"Broker" |
"other";

@oneOf
value:
805190000 |
805190001 |
805190002 |
805190003 |
805190004 |
805190008;
}
```

But that it not the same because with that approach invalid combinations could be created.

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Read the [docs](https://typespec.io/docs/).
- [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.