rst writer with --list-tables=true: fix not aligned indentation of table elements

[PhilipPartsch]

Explain the problem.
In reStructuredText (rst) specification the indentation of blocks are important.
Currently the generate elements in list-table rst directive are not indented by three spaces as the rest in our rst writer.
So rst parsers treat these parts as not aligned and so they are different blocks - instead as one.

Current output:
from

.. list-table::
   :widths: 36 36
   - 
      - HTTP header

         The HTTP header indicates that the HTTP method used is POST,
         ...

Expected output:

.. list-table::
   :widths: 36 36
   - 
      -  HTTP header

         The HTTP header indicates that the HTTP method used is POST,
         ...

As you can see the HTTP header is moved by one additional space.

Issue in the source code:
In rst writer we add only one space after - (- ). If we would write two spaces (- ), the parts of the documentation are aligned and are one rst block.

Alternative Solution:
We could even store, that here we do not have an indentation of three spaces, only two. So we indent the parts of this block only by two spaces.

Pandoc version?

3.4