Include data_validation in template

[Shettland]

A good feature for build_schema would be to already include data validation here, giving the users only a certain list of fields to choose from for each column as a dropdown menu. These should be based on the enums of the corresponding property from the processed schema: https://xlsxwriter.readthedocs.io/working_with_data_validation.html#working-with-data-validation

A nice addition could be to optionally lock the header and first column so they cannot be modified by the users. Reference on how to set a custom password and lock cells with add_format() here: https://xlsxwriter.readthedocs.io/format.html#set_locked

Here's a reference that I found on how to solve this task: https://stackoverflow.com/questions/51497731/openpyxl-is-it-possible-to-create-a-dropdown-menu-in-an-excel-sheet

Originally posted by @Shettland in #273 (comment)