filters.py: do_indent: ident filter can indent with arbitrary characters

filters.py: do_indent: ident filter can indent with arbitrary characters

Allow indention with generic characters, e.g. Tabs.

Implemenented the behavior requested in
https://github.com/pallets/jinja/pull/1167#issuecomment-612644701

The width param can be string or int, if it is string it's the raw
indention e.g. "\t". If it's int it's the number of spaces. In other
cases an FilterArgumentError is raised, to avoid confusion.