Enable NVS support for esp_schedule component (MEGH-6685)

[bbinet]

Answers checklist.

• I have read the Rainmaker documentation and the issue is not addressed there.
• I have updated my IDF branch (release/vX.Y) to the latest version and checked that the issue is present there. This is not applicable if you are using Rainmaker with Arduino.
• I have searched the Rainmaker forum and issue tracker for a similar issue and not found a similar issue.

General issue report

Schedules don't seem to be saved in NVS since enable_nvs is set to false here:

esp-rainmaker/components/esp_rainmaker/src/core/esp_rmaker_schedule.c

Line 969 in cb5f1dd

esp_schedule_init(false, NULL, NULL);

Why not set it to true by default, so that schedules are restored after device restart?
Is it safe to set it to true in my firmware code, or nvs support is not ready yet?

[shahpiyushv]

The nvs option of esp_schedule is meant to be used only when it is not being used from esp-rainmaker component.

When used from esp-rainmaker via the esp_rmaker_schedule_enable() call (which you will find in all examples and which is what you may be using too), since the schedule param itself is a persistent param, it gets stored in nvs and restored when the device reboots. Did it not work for you?

[bbinet]

Sorry, my bad. I read part of the code before having actually done any tests...

We need to add scheduling support to our own rainmaker-based firmware, and ensure our own code won't put device in deep sleep while it was supposed to be running to execute some scheduling jobs.
It would be great if rainmaker could expose an API function to retrieve the next datetime the device is supposed to execute a scheduled job, so that we can prevent device to deep sleep at this time.

[bbinet]

I may submit a pull request to add this feature if it sounds sensible to you.