Integrations: Add Hardware Wallet SDKs

[martineckardt]

Add a new category Hardware Wallets that list Ledger and Keystone and their SDKs. In the integration text put focus on showing that wallets or other apps can use these SDKs instead of high-level information about the hardware wallets. So the target group would be wallet-like applications.

Ledger

• Avalanche Ledger App
• Avalanche Ledger App Go SDK
• Avalanche Ledger App JS SDK

Keystone

We just gave them a grant to support the X-/P-Chain. So no information how to integrate yet, but should come in a couple months

• Firmware