Add per-package `coverage` enforcement mechanism

@pdhotems has requested that we enforce a minimum code coverage number, below which we will deny the pullrequest.

I didn't receive any specific feedback on the feature itself. I think the way I'd want this to work is to offer a pyproject.toml customization that will enable this behavior. That way nobody will be surprised.

Here is a section of the azure-ai-ml pyproject.toml

# existing config
[tool.azure-sdk-build]
mypy = true
pyright = false
type_check_samples = false
pylint = true
mindependency = false
latestdependency = false
black = true
# new keys
enforce_coverage = true
coverage_limit = 0.3 # the check will be <calculated_cov_%> <= <coverage_limit>

Where the overall coverage goal comes from coverage_limit, and enforce_coverage enables this behavior. Opt-in to start.

Comienza localizando cómo se leen las configuraciones de azure-ai-ml pyproject.toml [tool.azure-sdk-build] y dónde las comprobaciones de pull request calculan la cobertura. Define el comportamiento de activación explícita de enforce_coverage y coverage_limit, incluido lo que ocurre cuando la cobertura es igual o inferior al límite configurado, y verifica después el comportamiento con las pruebas de comprobación existentes del repositorio.