Standardize device and device group maintenance API

[rhinoau]

This PR standardises the behaviour of the devices and devicegroups maintenance API:

• defaults to immediate now() maintenance if no start given
• accepts scheduled maintenance start if given
• handles host not found errors cleanly
• documentation clarity

Prior, the two routines made different assumptions, devices could only have immediate maintenance, and basic errors were not handled for omitted data or device not found.

DO NOT DELETE THE UNDERLYING TEXT

Please note

Please read this information carefully. You can run ./lnms dev:check to check your code before submitting.

• Have you followed our code guidelines?
• If my Pull Request does some changes/fixes/enhancements in the WebUI, I have inserted a screenshot of it.
• If my Pull Request makes discovery/polling/yaml changes, I have added/updated test data.

Testers

If you would like to test this pull request then please run: ./scripts/github-apply <pr_id>, i.e ./scripts/github-apply 5926
After you are done testing, you can remove the changes with ./scripts/github-remove. If there are schema changes, you can ask on discord how to revert.

[librenms-bot]

This pull request has been mentioned on LibreNMS Community. There might be relevant details there:

https://community.librenms.org/t/api-api-v0-devicesgroups-name-maintenance-server-error-set-app-debug-true-to-see-details/19164/10

[murrant]

I would be a little more strict on this, since the two API endpoints were broken up until very recently, LGTM. Improved consistency is definitely welcome.

[librenms-bot]

This pull request has been mentioned on LibreNMS Community. There might be relevant details there:

https://community.librenms.org/t/api-functions/18593/3