Define the AccountPayments RPC endpoint and its request/response
messages in lit-accounts.proto. This endpoint allows querying
paginated payment history for a specific account.
Also update the frontend JS/TS proto sanitization script to map the
imported lnd.proto file to its flat directory path, fixing app build.
This commit introduces the structure for new endpoints in the accounts
subsystem, enabling balance adjustments by crediting or debiting a
specified amount. This contrasts with the existing `UpdateAccount`
implementation, which directly sets the balance to a fixed value.
For more details on the drawbacks of the current implementation, see
[issue #648](https://github.com/lightninglabs/lightning-terminal/issues/648).
The actual implementation of the endpoints will be introduced in
subsequent commits.
