Fixes RelativeLinkFilter for users that don't have access
to the project's repository

When post-processing relative links to absolute links
RelativeLinkFilter didn't take into consideration that
internal repository data could be exposed for users
that do not have repository access to the project.

This commit solves that by checking whether the user
can `download_code` at this repository, avoiding any
processing of this filter if the user can't.

Additionally, if we're processing for a group (
no project was given), we check if the user can
read it in order to expand the href as an extra.
That doesn't seem necessarily a breach now,
but an extra check doesn't hurt as after all
the user needs to be able to `read_group`.

Using the sed script from
https://gitlab.com/gitlab-org/gitlab-ce/issues/59758

Personal snippet uploads have neither a group nor a project. If a GitLab
instance were configured with a relative URL root (e.g. `/gitlab`), then
the Markdown filter would not include this root in the generated path.
We fix this by adding this root if there is no group or project.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56280

https://gitlab.com/gitlab-org/gitlab-ce/issues/52009

There are certain inputs that look like valid URIs that are accepted by URI
but not Addressable::URI. Handle the case where the latter fails.

Closes #41442

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true
Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

Signed-off-by: NRémy Coutable <remy@rymai.me>

    A lot of git operations were being repeated, for example, to build a url
    you would ask if the path was a Tree, which would call a recursive routine
    in Gitlab::Git::Tree#where, then ask if the path was a Blob, which would
    call a recursive routine at Gitlab::Git::Blob#find, making reference to
    the same git objects several times. Now we call Rugged::Tree#path, which
    allows us to determine the type of the path in one pass.

    Some other minor improvement added, like saving commonly used references
    instead of calculating them each time.

Prior, if we were viewing a blob at
`https://example.com/namespace/project/blob/master/doc/some-file.md` and
it contained a relative link such as `[README](../README.md)`, the
resulting link when viewing the blob would be:
`https://example.com/namespace/project/blob/README.md` which omits the
`master` ref, resulting in a 404.