Allow proper types for agent props

**Describe the bug**
The generic types for `Agent` enforces `Record` as bound for `Props`. This Record type requires subtypes to define an index signature for type `string`, which prevents using interfaces with well-defined properties.

**To Reproduce**
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
While the type could still *default* to `Record`, it should allow using proper interfaces that have no index signature.

**Screenshots**

This is the error reported by Typescript on a `getAgentsByName` call passing `{ props: config }` as third argument:

**Version:**
0.17.3

**Additional context**