feat(wallets): Move wallets API under customers

[vankiru]

Context

The PR implements api for /customers/:customer_external_id/wallets and /customers/:customer_external_id/wallets/:code/metadata endpoints.

Related PR: getlago/lago-api#4995

Description

The new customer wallets and metadata API looks like this 👇

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

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

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

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

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

And for the metadata:

# POST /customers/:customer_id/wallets/:wallet_code/metadata
client.customers.wallets.metadata.replace(customer_id, wallet_code, metadata)

# PATCH /customers/:customer_id/wallets/:wallet_code/metadata
client.customers.wallets.merge(customer_id, wallet_code, metadata)

# DELETE /customers/:customer_id/wallets/:wallet_code/metadata
client.customers.wallets.delete_all(customer_id, wallet_code)

# DELETE /customers/:customer_id/wallets/:wallet_code/metadata/:key
client.customers.wallets.delete_key(customer_id, wallet_code, key)

Nested Commands

Similar to Ruby, this PR introduces a few new nested mixins that add support for nested resources. They're pretty close to the single-resource mixins, with a couple of differences:

• update takes the resource ids first, and then the params as the last argument,

client.customers.wallets.update(customer_id, wallet_code, params)
# vs
client.customers.update(params, customer_id)

• the timeout option for all methods, and options for find_all, have to be passed as keyword arguments only

client.customers.wallets.get(customer_id, wallet_code, timeout=1.0)
client.customers.wallets.get_all(customer_id, options={"page": 1})