repoview: flag `server.view` as experimental
Ideally, the non-experimental version of `experimental.extra-filter-revs` will
cover the use case for `server.view=immutable` well enough than having to have
this dedicated configuration. Since `server.view` is not part of any release, I
would prefer to have it marked as experimental to avoid having it to support it
for ever.
repoview: move subsettable in a dedicated module
The dictionary got moved in `branchmap` to avoid import cycle. However, we are
about to needs it in repoview too. So we introduce a now module to define that
that mapping.
upgrade: support upgrade to/from zstd storage (
issue6088)
Now that we have an official config option for a shiny format improvement, we
better make it simple to migrate to/from it.