refactor(storage-manager): move prefix related functions in crate

[J-Loudet]

This change is motivated by the refactor of the Replication feature. In order to exchange metadata that can be processed by all Replicas, the key expressions associated with the data stored must be prefixed (when sent) and stripped (when received).

This commit exposes two functions, at the zenoh-plugin-storage-manager crate, that perform these operations.

The objective is to reuse these functions in the Replication refactor and, as we intend to move the Replication in its own crate, exposing them at the crate level makes it easier to then import them.

• plugins/zenoh-plugin-storage-manager/src/lib.rs:
  • moved there the strip_prefix function,
  • moved there the get_prefixed function and renamed it to prefix.
• plugins/zenoh-plugin-storage-manager/src/replica/mod.rs: updated the call to the previously named get_prefixed function.
• plugins/zenoh-plugin-storage-manager/src/replica/storage.rs:
  • removed the strip_prefix method,
  • removed the prefix function,
  • updated the call to strip_prefix and get_prefixed.