refactor: use fit-connect-baseimage

.gitlab-ci.yml

-.pre-deploy-uber-space-setup: &pre-deploy-uber-space-setup
-  - apk add rsync openssh-client
+.ssh-setup: &ssh-setup
   - eval $(ssh-agent -s)
   - echo "$CI_DEPLOYMENT_PRIVATE_KEY" | tr -d '\r' | ssh-add -
-  - mkdir --mode 700 -p ~/.ssh
   - echo "$UBERSPACE_KNOWN_HOST" >> ~/.ssh/known_hosts
 
 include:
@@ -36,7 +34,7 @@ build:
 
 upload:preview:
   stage: upload
-  image: alpine:latest
+  image: ${CI_REGISTRY}/fit-connect/baseimage:latest
   environment:
     name: preview/$CI_COMMIT_REF_NAME
     on_stop: stop:preview
@@ -47,14 +45,14 @@ upload:preview:
   rules:
     - if: $CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH
   before_script:
-    - *pre-deploy-uber-space-setup
+    - *ssh-setup
   script:
     - ssh -o CheckHostIP=no fitko@dorado.uberspace.de mkdir -p preview.docs.fitko.dev/fit-connect
     - rsync -rLvz --delete --checksum -e "ssh -o CheckHostIP=no" --ipv4 --progress ./build/. fitko@dorado.uberspace.de:preview.docs.fitko.dev/fit-connect/$CI_COMMIT_REF_SLUG
 
 upload:production:
   stage: upload
-  image: alpine:latest
+  image: ${CI_REGISTRY}/fit-connect/baseimage:latest
   environment:
     name: production
     url: https://docs.fitko.de/fit-connect/
@@ -63,7 +61,7 @@ upload:production:
   rules:
     - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
   before_script:
-    - *pre-deploy-uber-space-setup
+    - *ssh-setup
   script:
     - ssh -o CheckHostIP=no fitko@dorado.uberspace.de mkdir -p docs.fitko.de/fit-connect
     - rsync -rLvz --delete --checksum -e "ssh -o CheckHostIP=no" --ipv4 --progress ./build/. fitko@dorado.uberspace.de:docs.fitko.de/fit-connect
@@ -80,7 +78,7 @@ stop:preview:
     - if: $CI_MERGE_REQUEST_ID
       when: manual
   before_script:
-    - *pre-deploy-uber-space-setup
+    - *ssh-setup
   script:
     - ssh fitko@dorado.uberspace.de "rm -rf preview.docs.fitko.dev/fit-connect/$CI_COMMIT_REF_SLUG"