Write templates to specified path

[AlinaGoaga]

Closes #2215

What changed?
gitops create template template.yaml --values CLUSTER_NAME=ewq --export (go run cmd/gitops/main.go create template ...)

only renders to stdout. We want to respect the file paths returned and write out the yaml to those paths, relative to the --outDir flag. e.g:

gitops create template --outDir ./out --values CLUSTER_NAME=ewq should write out: ./out/clusters/ewq.yaml

How did you validate the change?
Tested with go run cmd/gitops/main.go create template cmd/gitops/app/create/templates/testdata/template.yaml --values RESOURCE_NAME=ewq NAMESPACE=default TEMPLATE_PATH=./ GIT_REPO_NAME=test GIT_REPO_NAMESPACE=default --outDir=./out

after updating template.yaml to:

resourcetemplates:
    - path: "/resources1/${RESOURCE_NAME}.yaml"
      content:
        - apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
          kind: Kustomization
          metadata:
            name: ${RESOURCE_NAME}
            namespace: ${NAMESPACE}
          spec:
            interval: 1h
            path: ${TEMPLATE_PATH}
            sourceRef:
              kind: GitRepository
              name: ${GIT_REPO_NAME}
              namespace: ${GIT_REPO_NAMESPACE}
    - path: "/resources2/${RESOURCE_NAME}.yaml"
      content:
        - apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
          kind: Kustomization
          metadata:
            name: ${RESOURCE_NAME}
            namespace: ${NAMESPACE}
          spec:
            interval: 1h
            path: ${TEMPLATE_PATH}
            sourceRef:
              kind: GitRepository
              name: ${GIT_REPO_NAME}
              namespace: ${GIT_REPO_NAMESPACE}

The directories and files that got created:

Documentation Changes
Need to update docs.

[sarataha]

LGTM! 🥇

[foot]

💯

[bigkevmcd]

Please use SecureJoin https://github.com/fluxcd/flux2/blob/9c3750613014b4b499675b231f7b08103ac5e8d1/pkg/manifestgen/manifest.go#L24 we're accepting data from a user, so we should make sure not to allow escapes!