Allowing creation of timesheet records with begin and end time

[vworldat]

I added --begin/-b and --end/-e options to the kimai start command. This would resolve both #7 as well as parts of #8 (no --end option for kimai stop yet).

Had to add a phpstan baseline to ignore errors caused by kimai/api-php declaring nullable getters as non-nullable.

[kevinpapst]

I did not test it, but look good to me.

Thanks @vworldat 👍