Bluetooth: provide struct bt_gatt_indicate_params to bt_gatt_indicate_func_t

[JordanYates]

Is your enhancement proposal related to a problem? Please describe.

As noted by the function documentation, bt_gatt_indicate is an asynchronous function, and therefore the struct bt_gatt_indicate_params provided to it must valid while it is active. The required lifetime of the struct bt_gatt_indicate_params is presumably until the member function bt_gatt_indicate_func_t is called (this is not specified). Currently, it is not possible to determine from the callback which struct bt_gatt_indicate_params is now available to be reused.

This is an issue when multiple indications need to be queued, with the structs allocated from some kernel mechanism (k_mem_slab or other), as there is no way to free the instances once they are no longer needed.

Describe the solution you'd like
const struct bt_gatt_attr *attr parameter to bt_gatt_indicate_func_t changed to struct bt_gatt_indicate_params *params.
The attr element is still accessible from the *params, but the params instance can also be freed in the callback.

Describe alternatives you've considered
None, there is no user data parameter or similar to retrieve the struct bt_gatt_indicate_params pointer from the completing indication.

[JordanYates]

Superseded by #29357