Modify to support dbt-core 1.6 and above

[syou6162]

Currently, dbt-osmosis supports a very wide range of dbt-core versions. As a result, there is code that diverges depending on the version of dbt-core, resulting in complexity and test case omissions. And Support level and end date for dbt 1.5 and below is End of Life.

• ref: https://docs.getdbt.com/docs/dbt-versions/core

This pull request explicitly limits the supported dbt-core versions so that dbt-osmosis can keep up with new dbt-core versions as they become available and remain highly maintainable.

• ref: https://github.com/z3z1ma/dbt-osmosis/pull/150/files#r1600410662

[syou6162]

@z3z1ma As I had received prior feedback in the comments, I have prepared a pull request with a modification to explicitly remove support for versions below 1.5 of dbt-core. Could you review it?

[z3z1ma]

LGTM, thanks so much @syou6162 🙇