**What**
- register a publishable API key through `medusa-js` i.e. define the key that will be sent with each request
**How**
- introduce KeyManager class which is used to share keys between medusa-js objects.
**Usage**
1. Set the key through the `Medusa` config
2. Set the key through `KeyManager` dynamically:
```ts
import { KeyManager } from "medusa-js"
KeyManager.registerPublishableApiKey("pk_123")
```
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RESOLVES CORE-794
9eafde07fe