change naming schema for the username and group

Hi,

It seems like naming a remote is subject to certain limitations as `groupadd` is executed ([potentially 32chars?](https://unix.stackexchange.com/questions/11477/what-are-the-allowed-group-names-for-groupadd)).

**Example**

```yaml
apiVersion: gitkube.sh/v1alpha1
kind: Remote
metadata:
name: app-remote
namespace: my-really-really-really-long-ns
```

```bash
k logs po/gitkubed
Setting up git remotes
Configuring : my-really-really-really-long-ns-app-remote
Adding user `my-really-really-really-long-ns-app-remote' ...
Adding new group `my-really-really-really-long-ns-app-remote' (1000) ...
groupadd: 'my-really-really-really-long-ns-app-remote' is not a valid group name
adduser: `/usr/sbin/groupadd -g 1000 my-really-really-really-long-ns-app-remote' returned error code 3. Exiting.
```

Is there any way to overwrite the computed `my-really-really-really-long-ns-app-remote` identifier so groupadd can run through?

No source file or test is named in the issue. Trace how the Remote namespace and name become the computed username and group identifier, then check the groupadd naming constraints shown in the example. Done means long names can be overridden or transformed into a valid identifier without breaking remote setup.

Written by the indexing model from the issue text.