Allow SampleResult#setEndTime be set in JSR223Sampler

[FSchumacher]

Issue #5733

Description

JSR223Sampler throws an exception, when the sampler has set the endTime of the sampleResult.

Motivation and Context

JSR223Sampler is often used to create results in a freestyle mode. So setting the endTime of a SampleResult should be allowed.

How Has This Been Tested?

Added a new Test class, that tests both paths setting and not setting the endTime on the SampleResult.

Screenshots (if appropriate):

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 not work as expected)

It is a bit hard to decide on this. I think of it as a bug fix.

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.