[lldb] Add a setting to not install the main executable

Summary:
Add setting target.auto-install-main-executable that controls whether
the main executable should be automatically installed when connected to
a remote platform even if it does not have an explicit install path
specified. The default is true as the current behaviour.

Reviewers: omjavaid, JDevlieghere, srhines, labath, clayborg

Reviewed By: clayborg

Subscribers: kevin.brodsky, lldb-commits, llvm-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D71761