[CBM] Add support for opening documentation from a "new" pre-defined location (single package support)

What's the issue?
'cbbackupmgr' uses/opens documentation which is stored in the '/opt/couchbase' directory by default. When we create a tools separate package, we need to maintain the ability to store/open these files so that users have access to the documentation.

What's the fix?
1) We need a new location where these man/html files are stored
2) We need to update the build process to correctly handle setting the path for the documentation at compile time. There is already logic for picking a different path based on an InstallType variable which is set at compile time.