Support for different types of config store backends

[sanfern]

L3afd supports file to store persistent configs, it's good to support different backends like db and kv store.

[dthaler]

@sanfern can you add more information that someone else could use to get started on this?

[satyaranjanp]

L3AFD stores the current ebpf program configs and keeps on updating these with each incoming 'update config' request. These configs are accessed during L3AFD restarts using the stored configurations. Currently L3AF uses local filesystem (configurable as filename: /var/l3afd/l3af-config.json) to store the configurations in json format. L3AFD can use other storage backends as well to store these persistent configs (KV store, nosql db, etc).