[FR] Add WebApps support to project_management

Start in the project_management package and compare the existing iOSApps and AndroidApps APIs with the proposed WebAppsService. Review the Firebase REST webApps resource and determine the complete API surface beyond metadata and config; done means WebApps support is exposed consistently with the existing platform services and covered by the relevant tests.

Is your feature request related to a problem? Please describe.
The project_management package miss API to work with webApps resource

Describe the solution you'd like
API to work with WebApps similar to the ones available for iOSApps and AndroidApps

Describe alternatives you've considered
The single alternative I considered was to use the REST requests by hands

Additional context
I implemented a bare minimum solution just extending _ProjectManagementService

from firebase_admin import project_management


class WebApp:
    def __init__(self, app_id, service) -> None:
        self._app_id = app_id
        self._service = service

    @property
    def app_id(self):
        return self._app_id

    def get_metadata(self):
        return self._service.get_web_app_metadata(self._app_id)

    def get_config(self):
        return self._service.get_web_app_config(self._app_id)


class WebAppsService(project_management._ProjectManagementService):
    WEB_APPS_RESOURCE_NAME = 'webApps'

    def __init__(self, app):
        super().__init__(app)

    def list_web_apps(self) -> list[WebApp]:
        return self._list_apps(
            platform_resource_name=WebAppsService.WEB_APPS_RESOURCE_NAME,
            app_class=WebApp
        )

    def get_web_app_metadata(self, app_id):
        path = '/v1beta1/projects/-/{0}/{1}'.format(
            WebAppsService.WEB_APPS_RESOURCE_NAME,
            app_id,
        )
        return self._make_request('get', path)

    def get_web_app_config(self, app_id):
        path = '/v1beta1/projects/-/{0}/{1}/config'.format(
            WebAppsService.WEB_APPS_RESOURCE_NAME,
            app_id,
        )
        return self._make_request('get', path)

but it can be completed with all APIs