Add experiment and execute functionality

[tornede]

Description

I added two functions.

1. A function to create a database without directly adding experiment instances called create_table.
2. A function to add a configuration to the database, and immediately execute it. Note that the status of the experiment is set to CREATED_FOR_EXECUTION, and immediately executed.

Motivation and Context

An additional state is useful for possible error handling. Otherwise the changes are motivated by the Feature Request.

Type 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 change)

How has This Been Tested?

• Database provider: MySQL and SQLITE
• Python version: 3.9
• Operating System: Linux Ubuntu

Does this Close/Impact Existing Issues?

This implementation fulfils the request

• Issue Feature Requests: Add new experiment, and start immidiately #189
  Due to documentation dependence, the implementation is not based on develop but rather Documentation for distributed execution #175

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