Improve migration framework and add migration 101 - Continued

[luisa-beerboom]

See #3548

What it is still lacking:

• including all adjacent collections into the replace tables
  • Migration handlier does probably not collect all additional views during migration setup.
• check that view and table names in trigger definitions are properly replaced for adjacent tables
• I didn't check the behaviour for foreign key constraints during migration
• In general tables and intermediate tables cannot be deleted before their views. Things like these shouldn't happen vaguely with 'IF EXISTS' or CASCADE to keep it explicit and specific to understand exactly what is being done.
• split logical segments of long functions into new functions
• Before migration does not setup the fkey constraints according to which migration tables were created and which should still point to origin tables. See TODO at line 128
  • For this write a check to assure that after migrate there exists a foreign key from an adjacent origin tables to a migration table.
  • In that area also drop the old constraint. See commented out code.
• Write check to assure that also for adjacent tables a migration view is created. Best case also compare to the correct view definition to assure that its pointing to existing migration tables and in all other cases to origin tables.
• does not nicely make use of additional_views information (for instance creation of real_replace_tables). There is a possibility to store that information analogously in its own column.
• BaseMigrationTestCase doesn't hold the cursor so it's always required to pass that to assert_content_not_none.
• Needs to properly check the recreation of views and triggers for collections like committee adjacent to origin tables like meeting
• check TODO at line 619 of migration handler
• TODO in test 101 line 61 may help to generalize some parts of the test setup.
• Does not assert the general functionality of the framework if the test for 101 is gone. Maybe we can find a solution by mocking or integrating it into the mig 100 test.
• There is the general problem of information getting lost in models yml between migrations. As get_replace_tables in migration_helper relies on that information, we may need specific alterations defined by each migration. One approach could be to set the information in the data definition function or create a function like this analogously to write the information lost into the version table either directly into the replace_tables column or its own. Another one would be to write such information into a data structure of the migration class. There was also the discussion about creating diffs from yml files.
• Needs a general code cleanup like variable names hopefully solved todos and code structure
• implement all changes including helper functions necessary for a migration like this: https://github.com/OpenSlides/openslides-meta/pull/372/changes and https://github.com/OpenSlides/openslides-vote-service/blob/feature/vote/Migration.md
• MigrationHandler.set_public_tables_read_only is broken (see TODO)