Feature add postgresql support

[TheoPascoli]

Summary:

This pull request adds support for PostgreSQL in addition to the existing MySQL support. To achieve this, a new environment variable sql_db_type has been introduced, allowing the user to choose between PostgreSQL and MySQL. By default, if the sql_db_type variable is not set, MySQL is selected.

Changes Made:

Database Selection:
    Introduced a new environment variable sql_db_type.
    Default behavior remains unchanged with MySQL being the default if sql_db_type is not specified.
Method Optimization:
    Modified the method 'check_sql_available' to improve its efficiency.
Insert Operation Adjustment:
    Changed the method for inserting data into the systems table because INSERT IGNORE is not supported in PostgreSQL. 
    For PostgreSQL, the query now uses INSERT INTO ... ON CONFLICT DO NOTHING.

Please let me know if there are any questions or further modifications required.

[JanMaartenvanDoorn]

Thanks and nice addition to openSTEF! I think many can benefit from postgresql support.

I found a few minor things we can improve. The most important one is that sql_db_type is now defined as a string. As there are only two options and different forms (lower and upper) are used throughout the code I think it is nice to implement is as an enum (https://www.geeksforgeeks.org/enum-in-python/). This way we get a bit more control and validation.

In addition, I see that there are conflicts with the main branch, please resolve these as well.

Let me know if you have questions about this.

[alicecaron]

sql_db_type

I have:

• updated the main branch and rebased on it.
• created a new Enum: SupportedSqlTypes fot the available sql engines
• added unit tests

Please let me know if you see anything else to change

[JanMaartenvanDoorn]

@alicecaron Looks good, I see that black is failing though. You can probably fix this by running black . in the root of the repository and committing the changes.

[alicecaron]

@alicecaron Looks good, I see that black is failing though. You can probably fix this by running black . in the root of the repository and committing the changes.

Yes! I ran black on a new commit, it should be ok now @JanMaartenvanDoorn

[JanMaartenvanDoorn]

@alicecaron Looks good now!