Add Installation flavour configuration files

Add Installation flavour configuration files

rAppmanager and standalone-nonrtric flavour configuration files have been added to the helm-override directory.
Each flavour configuration should have onap-flavour-config.yaml and oran-flavour-config.yaml files.
onap-override.yaml and oran-override.yaml from default flavour is considered as a base configuration file for the respective flavour.
The onap-flavour-config.yaml and oran-flavour-config.yaml files are used to override the base configuration files.
During the installation, the appropriate flavour configuration files will be applied on top of the base configuration files.

Issue-ID: NONRTRIC-1082
Change-Id: I9ad3427ce2185cac5c185e3c81d701b8504cfde6
Signed-off-by: aravind.est <aravindhan.a@est.tech>