Use subparsers in the notifications command

We currently use the `--actions` parameter to define what to do, but this has increased over time and since `--actions` is a required parameter, we turned it into subcommands but without much organization. We should split it into subparsers and delegate each action to a defined function.

Example code for subparsers:
```python
from django.core.management.base import BaseCommand
from kernelCI_app.helpers.logger import out

class Command(BaseCommand):
help = "Test command for subparsers"

def add_arguments(self, parser):
subparsers = parser.add_subparsers(
title="action",
help="Available actions",
)
parser_function = subparsers.add_parser(
'function',
help='Execute _function'
)
parser_function.set_defaults(func=self._function)

second_function = subparsers.add_parser(
'second_action',
help='Execute _second_action'
)
second_function.set_defaults(func=self._second_action)

second_function.add_argument(
'--option',
type=str,
help='An example option for the second action',
)

def handle(
self,
*args,
**options,
):
out("Handle executed")
func = options["func"]
func(*args, **options)

def _function(self, *args, **options):
print(" ~ 🔍 _function (39) - options: %s" % options)
print("Function executed")

def _second_action(self, *args, option, **options):
print(" ~ 🔍 _second_action (44) - option: %s" % option)
print(" ~ 🔍 _second_action (42) - options: %s" % options)
print("Second action executed")

```

Start by locating the notifications management command and reading how the required --actions parameter currently dispatches work. Identify each existing action and its options, then verify that the command uses organized subparsers with a defined function for every action and that each action still receives its required arguments.

Written by the indexing model from the issue text.