Do not force creation of _cargo-index repo on publish (#27266)

Do not force creation of _cargo-index repo on publish (#27266)

Hello there,
Cargo Index over HTTP is now prefered over git for package updates: we
should not force users who do not need the GIT repo to have the repo
created/updated on each publish (it can still be created in the packages
settings).

The current behavior when publishing is to check if the repo exist and
create it on the fly if not, then update it's content.
Cargo HTTP Index does not rely on the repo itself so this will be
useless for everyone not using the git protocol for cargo registry.

This PR only disable the creation on the fly of the repo when publishing
a crate.

This is linked to #26844 (error 500 when trying to publish a crate if
user is missing write access to the repo) because it's now optional.

---------

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>