Bugfix of issues related to resultfield definition and processing

[LukasFehring]

Description

I finished 3 issues related to resultfield definition and processing that caused problems for users.

Motivation and Context

• PyExperimenterwith invalid configuration files have terminated with an error, without giving further information about the issue (Improve handling of configuration file and their invalidity #139).
• Processing results of PyExperimenter terminated with an error if a given resultfield was not defined in the configuration file and therefore was not covered in the database. Unfortunately, no information was given which field caused the problem (Improve processing information of ResultProcessor #140).
• Resultfields have been mandatory, preventing users to execute experiments without the need of resultfields (Allow configurations without resultfields #89)

Type Of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How has This Been Tested?

• Database provider: MySQL and SQLite
• Python version: 3.9.12
• Operating System: Ubuntu, MacOSX

Executed testcases, added minor testcases and executed examples. Also double checked that the checks for the existence of result/logtable columns work, by adapting own_functions in the notebook

All tests have been executed.

Does this Close/Impact Existing Issues?

• Issue Improve handling of configuration file and their invalidity #139
• Issue Improve processing information of ResultProcessor #140
• Issue Allow configurations without resultfields #89

Checklist

• My change is based on the latest stage of the develop branch.
• My change required a change of the documentation, which has been done.
• I checked that the documentation can be build, visualizes everything as expected, and does not contain any warnings.
• I have added/adapted tests to cover my changes.
• The tests can be executed successfully.
• The notebooks can be executed successfully.
• The notebooks can be executed with mysql as provider.
• I have added a description of the changes to CHANGELOG.rst.

[tornede]

LGTM except the log message changes mentioned above

[tornede]

LGTM