Improve support for gitea instances not running as root or uid 1000 (#266)

## Context

PR #259 introduced support for running Gitea as a uid different than 1000 (git) or 0 (root).

## Problem

In init_directory_structure.sh, there is a "chown 1000:1000" on /tmp/gitea.
This chown only works when running as root or when the target directory is already owned by uid 1000.

As a result, the init container "init-directories" fails on startup when running Gitea with a uid different from 0 or 1000.

Initially, I worked around it by implementing an "initPreScript". But it would make user's life easier if we can make it work out-of-the-box.

## Resolution

I'm taking model on the chown a few lines above that depends on the value of image.rootless. Since the chown only works on default (root) image and is useless on rootless image, there is no need to run it on rootless image.

Co-authored-by: Nicolas MASSE <nicolas.masse@itix.fr>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/266
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-authored-by: nmasse-itix <nmasse-itix@noreply.gitea.io>
Co-committed-by: nmasse-itix <nmasse-itix@noreply.gitea.io>

templates/gitea/init.yaml

@@ -30,7 +30,9 @@ stringData:
 
     # prepare temp directory structure
     mkdir -p "${GITEA_TEMP}"
+    {{- if not .Values.image.rootless }}
     chown 1000:1000 "${GITEA_TEMP}"
+    {{- end }}
     chmod ug+rwx "${GITEA_TEMP}"
 
   configure_gitea.sh: |-