Allow customization of post-template block markup

[allysonsouza]

What problem does this address?

While developing a custom posts listing section, sometimes we don't want or it's not correct to display it as an unordered list. For example, I'm facing a scenario on a project where I want to display each post entry as a row on a table, and it's not easy to filter/modify the <ul>/<li> markup being generated by post-template block.

What is your proposed solution?

I think some filters to determine wrapper_element/items_element could be helpful into the post-template/index.php