more options for future times validation

[kevinpapst]

Description

Currently there is a boolean rule to disallow future times.

This PR (which is not yet done) adds more options, e.g. to

• disallow starting in the future
• disallow ending in the future
• allow starting now (or in the past) and ending in the future

TODO validator/translations/more options

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I verified that my code applies to the guidelines (composer code-check)
• I updated the documentation (see here)
• I agree that this code is used in Kimai (see license)

[CLAassistant]

All committers have signed the CLA.