Function isCmcdV1Key

isCmcdV1Key(key: string): key is keyof Cmcd
Filter function for CMCD v1 keys.
Parameters
- key: string
  The CMCD key to filter.
Returns key is keyof Cmcd
true if the key should be included, false otherwise.
Example
```
equal(isCmcdV1Key('br'), true)
equal(isCmcdV1Key('e'), false)
```
- Defined in cmcd/src/isCmcdV1Key.ts:17