Adopt Pester 5

[nvarscar]

Reorganize tests:

• Should be universal and use the same test code for every RDBMS. The script code should still be different obviously. So, some kind of Setup function that does prepare/cleanup tasks based on provided RDBMS? Or perhaps, import sql code as variables.
• Group tests in folders: functional, common. Functional are to support parametrization (RDBMS type), common should be only run once and doesn't have parameters
• Improve invocation scripts to support the above
• Adjust code according to Pester 5 standards and remove all the code that is defined outside of the test body (It, Before, After).
• Use Pester -Skip to skip the tests not supported in a particular RDBMS
• Use test cases for similar tests
• Remove legacy syntax (-Be instead of Be, etc)

[nvarscar]

Closed by #152