ACLP: Remove content field from list alert channels response

[shkaruna]

📝 Description

Remove content field from list alert channels response.
content field is replaced with details.
Ticket: DPS-41868

✔️ 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 test:

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

2. Run Monitor alert channels unit tests:

   python -m pytest -q -s -v test/unit/objects/monitor_test.py::MonitorTest::test_alert_channels
   =============================================================== 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 1 item

test/unit/objects/monitor_test.py .

================================================================ 1 passed in 0.13s =================================================================

Integration test:
#if you have PAT token with write access only to Monitor and read for rest of the services for integration
export SKIP_E2E_FIREWALL=1 # optional: skip firewall to use fixture
export LINODE_TOKEN="YOUR_REAL_TOKEN" # required for integration
python -m pytest test/integration/models/monitor/test_monitor.py::test_integration_create_get_update_delete_alert_definition -q -s
.
1 passed in 12.18s

[shkaruna]

@satkumar-akamai : Please review