Rework config file handling

These changes allow for a local rules file that will be preserved across
upgrades and allows the main rules file to be overwritten across upgrades.

- Move all config/rules files below /etc/falco/
- Add a "local rules" file /etc/falco/falco_rules.local.yaml. The intent
  is that it contains modifications/deltas to the main rules file
  /etc/falco/falco_rules.yaml. The main falco_rules.yaml should be
  treated as immutable.
- All config files are flagged so they are not overwritten on upgrade.
- Change the handling of the config item "rules_file" in falco.yaml to
  allow a list of files. By default, this list contains:
  [/etc/falco/falco_rules.yaml, /etc/falco/falco_rules.local.yaml].

Also change rpm/debian packaging to ensure that the above files are
preserved across upgrades:

- Use relative paths for share/bin dirs. This ensures that when packaged
  as rpms they won't be flagged as config files.
- Add CMAKE_INSTALL_PREFIX to FALCO_ENGINE_LUA_DIR now that it's relative.
- In debian packaging, flag
  /etc/falco/{falco.yaml,falco_rules.yaml,falco_rules.local.yaml} as
  conffiles. That way they are preserved across upgrades if modified.
- In rpm packaging when using cmake, any files installed with an
  absolute path are automatically flagged as %config. The only files
  directly installed are now the config files, so that addresses the problem.

Add CMAKE_INSTALL_PREFIX to lua dir.

userspace/engine/config_falco_engine.h.in

@@ -18,5 +18,5 @@ along with falco.  If not, see <http://www.gnu.org/licenses/>.
 
 #pragma once
 
-#define FALCO_ENGINE_LUA_DIR "${FALCO_SHARE_DIR}/lua/"
+#define FALCO_ENGINE_LUA_DIR "${CMAKE_INSTALL_PREFIX}/${FALCO_SHARE_DIR}/lua/"
 #define FALCO_ENGINE_SOURCE_LUA_DIR "${PROJECT_SOURCE_DIR}/../falco/userspace/engine/lua/"