[JAB1305]

Previous status code were not in agreement with the respective specification.

This change adjusts the HTTP status codes.

Fixes #625

[s-heppner]

This needs to be adapted when #627 is merged.

[zrgt]

The spec defines PostAllAssetLinksById as "Creates or replaces all asset links associated to the Asset Administration Shell" (spec). The endpoint currently merges the posted links into the existing ones, and test_post_is_additive asserts that, see #669.

Since this PR already aligns this endpoint with the spec, could it also replace the links instead of merging them, and flip test_post_is_additive?

[zrgt]

Related to the requested change for #669: both handlers in this PR also maintain the reverse index (asset_id_to_aas_ids) themselves, via the private _add_aas_id_to_specific_asset_id() and a loop over the store's dict that leaves empty sets behind. Moving that into add_specific_asset_ids_to_aas() / delete_specific_asset_ids_by_aas_id() would make the replace logic a single place to change, see #669 (comment).