dirmgr: Expopse DirMgrStore

This is an opaque type, and all you can do with it is make one, and pass it to the DirMgr and BridgeDescMgr constructors.

This is needed for #631 (closed). The solution is not the one mentioned in #631 (comment 2853665) and is in fact simpler than that.

The branch is on top of !845 (merged) which I think is unblocked, but has not yet been merged.

assigned to @Diziet

requested review from @nickm

This LGTM. Nice to see the boilerplate impl disappear.

approved this merge request

Please feel free to merge this as appropriate once !845 (merged) is to your liking.

merged

mentioned in commit 58fc19dc