Add DAP log level parameter

Add DAP log level parameter

This adds a new parameter to control the DAP logging level.  By
default, "expected" exceptions are not logged, but the parameter lets
the user change this when more logging is desired.

This also changes a couple of spots to avoid logging the stack trace
for a DAPException.

This patch also documents the existing DAP logging parameter.  I
forgot to document this before.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-By: Kévin Le Gouguec <legouguec@adacore.com>