Implement STM32 RTC alarms

[markus-k]

Implements setting up and awaiting RTC alarms.

Example:

    let mut rtc = Rtc::new(p.RTC, RtcConfig::default());

    rtc.set_alarm(
        Alarm::A,
        RtcAlarmMatch {
            subsecond: None,
            second: None,
            minute: None,
            hour: None,
            hour_is_pm: false,
            date: None,
        },
    );

    // would wait until the second increments
    rtc.wait_for_alarm(Alarm::A).await;

Still quite WIP as the different stm32 lines differ quite a bit in EXTI/IRQs. So far tested on STM32 G0, G4, L0 and F3.

Posting this here already to gather some feedback, if there is any. Maybe the actual implementation should be moved to the v2/v3 modules as they do differ quite a bit and need lots of conditionals.

Needs embassy-rs/stm32-data#565 and embassy-rs/stm32-data#564 merged and released in stm32-data.

[Dirbaio]

Needs embassy-rs/stm32-data#565 and embassy-rs/stm32-data#564 merged and released in stm32-data.

now that they're merged, switch embassy-stm32 to use stm32-data from git (uncomment the two lines, update the commit hash). We do stm32-metapac+embassy-stm32 releases at the same time.