feat(alerting): Add wallet alerts API

[vankiru]

Context

The PR implements api for wallet alerts. It relies on the implementation of Nested Commands introduced in #366.

Related PR: getlago/lago-api#4925

Description

The wallet alerts API looks like this 👇

# GET /customers/:customer_id/wallets/:wallet_code/alerts
client.customers.wallets.alerts.get_all(customer_id, wallet_code)
client.customers.wallets.alerts.get_all(customer_id, wallet_code, options={"page": 1, "per_page": 100})

# POST /customers/:customer_id/wallets/alerts
client.customers.wallets.alerts.create(customer_id, wallet_code, params)

# GET /customers/:customer_id/wallets/:wallet_code/alerts/:alert_code
client.customers.wallets.alerts.get(customer_id, wallet_code, alert_code)

# PATCH /customers/:customer_id/wallets/:wallet_code/alerts/:alert_code
client.customers.wallets.alerts.update(customer_id, wallet_code, alert_code, params)

# DELETE /customers/:customer_id/wallets/:wallet_code/alerts/:alert_code
client.customers.wallets.alerts.destroy(customer_id, wallet_code, alert_code)