Make update object metadata API atomic

[arielshaqed]

Protect updating object metadata on an existing entry to be safe against concurrent modifications, deletions, and commits and merges to the branch. This is a bit tricky because it needs to work for both committed and staged objects.

Fixes #8262 - a race that would give an odd result if update object metadata managed to lose against concurrent delete and uncommitted GC, or potentially merges into the branch.

[github-actions[bot]]

E2E Test Results - Quickstart

[github-actions[bot]]

E2E Test Results - DynamoDB Local - Local Block Adapter

[github-actions[bot]]

🎊 PR Preview bb6c44428e67ed789e6fca8a960063a4bb4fd7e0 has been successfully built and deployed to https://treeverse-lakeFS-preview-pr-8264.surge.sh

🕐 Build time: 0.01s

_{🤖 By surge-preview}

[arielshaqed]

Reviewers: I know that tests fail. Please review anyway, we will likely need >1 round -- and these will be easy enough to fix, and not in the areas modified in this PR.

[arielshaqed]

LookED good to Nir 😭

[N-o-Z]

LookED good to Nir 😭

I'll review it today 😃

[arielshaqed]

ObMeme: