docs: TestBench Load Testing tool

[tltv]

Adds new article documenting TestBench Load Testing tool.

[github-actions]

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[caalador]

Added feature that is not yet documented is that recording generates csv files for values that can be expanded to have random input for users.

Sample generated file crud-example-data.csv gets the content:

input_1,input_2,input_3,input_4,input_5,input_6,input_7
TestFirstName,TestLastName,test@example.com,123456789,1934-01-01,Vaadin Expert,Model

Adding rows will make the test use random rows for different users and this can be used to lessen impact with duplicate inputs.

Not adding anything the testers will run with the same data as recorded.