Align z_hello_locators signature with zenoh-c

[sashacmc]

Describe the release item

Currently in zenoh-c we have
void z_hello_locators(const struct z_loaned_hello_t *this_, struct z_owned_string_array_t *locators_out);
but in zenoh-pico we have
const z_loaned_string_array_t *z_hello_locators(const z_loaned_hello_t *hello);
Because in zenoh-pico we already have an object but in zenoh-c we should create it.
For API alignment we should rename current zenoh-pico method to zp_hello_locators (to allow make a call without additional overhead) and create z_hello_locators with the same signature as in zenoh-c (to have aligned API)