Add force_class option

[multimeric]

The current logic is that, if a table has no primary key, it doesn't use the declarative class generator. However, sqlite has the hidden rowid column which acts as a primary key. For this reason, I want to generate a dataclass and then add rowid as the primary key so that I get all the nice type safety of a dataclass. There are probably also other use cases for ignoring this rule.

Thus, this PR adds a new option called force_class that will generate a dataclass even if there is no obvious primary key.

[DevkumarPatel]

@multimeric when are we expecting this to go to production?.

[multimeric]

I don't follow. You can install directly from my fork if you want.

[agronholm]

The problem is that ORM classes don't function at all without primary keys. It won't work, period.

[agronholm]

If there is a "hidden" column, the ORM needs to know about it. Not declaring a primary key won't work.

[multimeric]

I think my logic in making this pull request was that you get the sqlacodegen to generate all of the columns and put it into a class, and then you manually modify the code to add the hidden rowid column as a primary key. I could have modified the generator to just add rowid using a flag, but that would have been an SQLite-specific change and thought that this was more generic.