feat: Add possibility to change orientation of column headers

[andreas-vester]

Prework

• Read and abide by the great_tables code of conduct and contributing guidelines.
• Search for duplicates among the existing issues (both open and closed).

Proposal

I suggest to introduce the possibility of changing the orientation of column headers (measured in degrees). If you have a large number of columns, it makes sense to change the orientation by 45° or 90°.