Exception for shared mem

[SirTobias]

Issue https://github.com/Project-OSRM/osrm-backend/issues/5998

Give reasonable messages for the exceptions of Boost that at least some messages pop up if the shared memory directory cannot be created or initialized.

Tasklist

• [x ] CHANGELOG.md entry (How to write a changelog entry)
• [-] update relevant Wiki pages -> imho not relevant
• [- ] add tests (see testing documentation - imho not relevant
• [ ] review
• [ ] adjust for comments
• [ ] cherry pick to release branch