feat: add ACLP list entities method

[shkaruna]

📝 Description

1. Update ACLP monitor AlertDefinition struct. Add scope & region fields.
2. Add entity envelope in AlertDefinition for GET, POST and PUT API responses.

"entities":` { // empty dict for region and account scope alert
"url":"/monitor/services/{service_type}/alert-definitions/{id}/entities",
  "count": integer,
 "has_more_resources": boolean
 }

3. Add new method to list entities.
   API: GET /monitor/services/{service_type}/alert-definitions/{id}/entities

JIRA: DPS-41869

✔️ How to Test

What are the steps to reproduce the issue or verify the changes?
Not applicable

How do I run the relevant unit/integration tests?

Prerequisites:
Clone the repository
Prepare environment (zsh / macOS)

Create and activate venv:
python3 -m venv .venv
source .venv/bin/activate

install deps
python -m pip install --upgrade pip

Install runtime dependencies:
pip3 install requests polling deprecated

Install dev/test extras
pip3 install -e '.[dev,test]'

test deps
pip3 install pytest mock httpretty pytest-rerunfailures

Unit tests:

1. Run all unit tests:
   python -m pytest test/unit -q

2. Run Monitor alert definition unit tests:
   python -m pytest test/unit/groups/monitor_api_test.py -q -s -v
   =============================================================== test session starts ================================================================
   platform linux -- Python 3.10.12, pytest-9.0.2, pluggy-1.6.0
   rootdir: /home/shkaruna/sdk/linode_api4-python
   configfile: pyproject.toml
   plugins: anyio-4.12.1, rerunfailures-16.1
   collected 4 items

test/unit/groups/monitor_api_test.py ....

================================================================ 4 passed in 0.11s =================================================================

Integration tests: (TODO: API is not live in devcloud & production)

[shkaruna]

@satkumar-akamai : Please review