Add custom start stop time support for test steps

[AndreyVChernykh]

• [ ] Sign Allure CLA
• [ ] Provide unit tests

Hello! In our testing solution, we need to specify the start and stop times for the testing steps. The added logic shouldn't break anything and makes the Allure more flexible. Thanks!

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: AndreyVChernykh
:x: Andrey Chernykh

---

Andrey Chernykh seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}