Remove the `--unsafe-pruning` CLI-argument (step 1) (#10995)

* sc-client-db: utils::open_database(...) — return OpenDbError so that the caller could tell the `OpenDbError::DoesNotExist` clearly

* sc-client-db: utils::open_database(..) — accept the `create: bool` argument

* sc-client-db: pruning — optional argument in the DatabaseSettings

* sc-state-db: Split `Error<E>` into separate `Error<E>` and `StateDbError`

* StateDb::open: choose the pruning-mode depending on the requested and stored values

* sc-state-db: test for different combinations of stored and requested pruning-modes

* CLI-argument: mark the unsafe-pruning as deprecated

* Fix tests

* tests: do not specify --pruning when running the substrate over the existing storage

* fix types for benches

* cargo fmt

* Check whether the pruning-mode and sync-mode are compatible

* cargo fmt

* parity-db: 0.3.11 -> 0.3.12

* sc-state-db: MetaDb::set_meta — a better doc-test

* cargo fmt

* make MetaDb read-only again!

* Remove the stray newline (and run the CI once again please)

* Last nitpicks

* A more comprehensive error message