clonebundle: add a `filter_bundle_url` function
This function does nothing by default, but give extension the opportunity to
alter the URL, typically, this could be used to inject authentication token when
serving clone bundle for private repositories.
clonebundles: move the manifest reading in a dedicated function
We are about to make the logic more advanced to help hosting solution, so we
need to centralize it first.
doc: format argument for date uses strftime format string (
issue6818)
clonebundles: filter out invalid schemes instead of failing on them
Previously, an invalid clonebundle scheme would result in a failed
clone. By specifying a list of schemes we support,
we can make sure adding a new scheme (like the one for inline clonebundles)
does not result in clones failing for older clients.