[lldb/Interpreter] Add setting to set session transcript save directory

This patch introduces a new interpreter setting
`interpreter.save-session-directory` so the user can specify a directory
where the session transcripts will be saved.

If not set, the session transcript are saved on a temporary file.

rdar://72902842

Differential Revision: https://reviews.llvm.org/D105030



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>