Document multiple instances of same provider

[Bilge]

Although we normally add a provider to the container by its class name and expect a single instance of each provider in the container, there are many valid use cases for adding the same provider multiple times. Document these use cases with examples and how-tos.

Often, we may operate multiple accounts with a given provider for various reasons. Examples:

• Multiple Stripe accounts for handling payments in different currencies
• Multiple Discord bots to leverage separate request rate limits