Added functionality to select type of certificate to be installed from the Settings app

This is part of the changes to improve the UX and language for installing certificates.
Previously, the different types of certificate used the same installation flow. This CL
introduces a new settings page, where the type of certificate to be installed can be selected.

Bug: 139173976
Test: Atest com.android.settings.security
      manual testing from Settings by selecting the certificate type
	preference and ensuring the installation flow still worked as expected.

Change-Id: Iea7c91aa3801e429f0e22d29469958f4151b3cba