feat(battery): Add Kconfig setting for battery level report interval

[caksoylar]

Makes the interval between BAS GATT reports for battery level configurable using a new CONFIG_ZMK_BATTERY_REPORT_INTERVAL setting. Related: #1273 (comment)

There are a few decisions I made that I am not 100% sure of, comments welcome:

• Location of Kconfig: right now this is under the battery driver, but it could be under app/Kconfig (in a new submenu under "Basic keyboard setup"?) or is there a better spot?
• Name of setting: I didn't mention BAS GATT since it is not very familiar to users. Should it have "level" in the name?
• Should the delay until first report also be configurable, or equal to the interval? I thought there isn't much use in making this configurable and 1 minute seems like a good value.
• Unit of interval: Minutes might be too coarse, milliseconds might be too fine, so I chose seconds.

[petejohanson]

Thanks!

There are a few decisions I made that I am not 100% sure of, comments welcome:

* Location of Kconfig: right now this is under the battery driver, but it could be under `app/Kconfig` (in a new submenu under "Basic keyboard setup"?) or is there a better spot?

Should definitely not be with the driver, since is app code consuming the driver. app/Kconfig somewhere is good.

* Name of setting: I didn't mention BAS GATT since it is not very familiar to users. Should it have "level" in the name?

I think the name you used is fine, IMHO.

* Should the delay until first report also be configurable, or equal to the interval? I thought there isn't much use in making this configurable and 1 minute seems like a good value.

I wouldn't complicate it that much. Just one setting is fine.

* Unit of interval: Minutes might be too coarse, milliseconds might be too fine, so I chose seconds.

Agreed on seconds being the right unit here.

[caksoylar]

Thanks for the comments! I moved the setting to app/Kconfig under the Advanced submenu, which sounded appropriate.

[petejohanson]

LGTM! Thanks!