new: Add support for Parent/Child account switching

[zliang-akamai]

📝 Description

This PR is for adding support of the parent/child account switching API endpoints.

✔️ How to Test

Automated Testing

Integration Testing

export LINODE_API_URL=https://the.dev.api.url/v4beta
export LINODE_API_CA=/path/to/your/alpha/ca.pem
export LINODE_TOKEN=YOUR_ALPHA_TOKEN
make TEST_CASE=test_list_child_accounts testint

Unit Testing

tox

Manual Testing

from linode_api4 import LinodeClient
client = LinodeClient(
    token="your_token",
    base_url="https://the.dev.api.url/v4beta",
    ca_path="/path/to/your/alpha/ca.pem"
)

child_accounts = client.account.child_accounts()
print(child_accounts)
token = child_accounts[0].create_token()
print(token)