change section detection to only require that line starts with the header instead of matching it

[kkotenko]

Per documentation of RF 7.0 https://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#test-data-sections:

"The header row can contain also other data than the actual section header. The extra data must be separated from the section header using the data format dependent separator, typically two or more spaces. These extra headers are ignored at parsing time, but they can be used for documenting purposes. This is especially useful when creating test cases using the data-driven style."

For simplicity, I have chosen to ignore the constraint that there must be a separator.

The practical application is, indeed, data-driven style tests.

[trannghia190]

got your idea, I added some code for it