Support STM32L1x Stop and Standby low power modes

[Oleh-Kravchenko]

Summary

Zephyr Project doesn't support low-power modes available in STM32L1x

Describe the solution you'd like

Implement Stop and Standby low-power modes.

Alternatives

N/A

Additional Context

N/A

[Oleh-Kravchenko]

Please assign to me 🫡, I'm already working on it.

P.S.
Require revert of 5a279d9, issue reported by #92461

[mathieuchopstm]

ping #81119