While gitlab-shell currently has a major version of v14, the module path
it exposes is not using that major version like it is required by the Go
standard. This makes it impossible for dependents to import gitlab-shell
as a dependency without using a commit as version.

Fix this by changing the module path of gitlab-shell to instead be
`gitlab.com/gitlab-org/gitlab-shell/v14` and adjust all imports
accordingly.

Changelog: fixed

Geo SSH proxy push currently impossible when the only
action that happens is branch removal. This fix
works in a way that it waits for flush packet from git
and then checks pkt lines to determine is pack data is expected.
The thing is that git doesnt send pack data when only
branch removal happens. Explanation is in
https://gitlab.com/gitlab-org/gitlab/-/issues/330494

In this case we don't need to propagate cleanup
function. It simplifies the code.

Previously, gitlab-shell did not pass a context through the application.
Correlation IDs were generated down the call stack instead of passed
around from the start execution.

This has several potential downsides:

1. It's easier for programming mistakes to be made in future that lead
to multiple correlation IDs being generated for a single request.
2. Correlation IDs cannot be passed in from upstream requests
3. Other advantages of context passing, such as distributed tracing is
not possible.

This commit changes the behavior:

1. Extract the correlation ID from the environment at the start of
the application.
2. If no correlation ID exists, generate a random one.
3. Pass the correlation ID to the GitLabNet API requests.

This change also enables other clients of GitLabNet (e.g. Gitaly) to
pass along the correlation ID in the internal API requests
(https://gitlab.com/gitlab-org/gitaly/-/issues/2725).

Fixes https://gitlab.com/gitlab-org/gitlab-shell/-/issues/474

We'll reuse this module for uploadpack in the future

Other functions are still expecting for `CommandArgs` instead
of `Shell`. They should be expecting `commandargs.Shell` now
since it has been renamed.