Rename pydocstyle.max-doc-length to max-doc-width

[MichaReiser]

Rename pydocstyle.max-doc-length to doc-width to align with other text width options and clarify that the option is about the text width and not character or byte length.

The max-doc-length option should act as an alias but Ruff should warn and hint users towards migrating to the new option.

[ngnpope]

Wondering whether the max- prefix is relevant? 🤔

If we are going for line-width, as the general line width value (without max-), would doc-line-width make more sense?