Make the `bee-storage` trait names "less surprising"

[pvdrz]

Description

We have the following access operations fetch, delete, exist, clear and we should consider renaming it to something more consistent with the standard library.

Motivation

Most of the standard library collections have the following basic operations: get, remove, contains, truncate. We should consider renaming the access traits.

Are you planning to do it yourself in a pull request?

Yes