Automatically create HELM_GIT_*_CACHE folders

[lucasfcnunes]

Helm version: version.BuildInfo{Version:"v3.15.4", GitCommit:"fa9efb07d9d8debbb4306d72af76a383895aa8c4", GitTreeState:"clean", GoVersion:"go1.22.6"}
helm-git version: 0.15.1
Git version: 2.46.0

Steps To Reproduce

1. HELM_GIT_DEBUG=1 HELM_GIT_REPO_CACHE='~/.cache/helm/git-helm/repo' HELM_GIT_CHART_CACHE='~/.cache/helm/git-helm/chart' helm repo add wazuh-helm 'git+https://github.com/lucasfcnunes/wazuh-helm@?ref=v0.0.1' --force-update

Link to chart repository: https://github.com/lucasfcnunes/wazuh-helm/tree/v0.0.1

The current behavior

Debug[196768] in plugin 'helm-git': repo: https://github.com/lucasfcnunes/wazuh-helm ref: v0.0.1 path:  file: index.yaml sparse: 1 depupdate: 1 package: 1
Debug[196768] in plugin 'helm-git': helm_repo_uri: git+https://github.com/lucasfcnunes/wazuh-helm@?ref=v0.0.1&sparse=1&depupdate=1&package=1
Debug[196768] in plugin 'helm-git': Helm request not found in cache ~/.cache/helm/git-helm/chart/759d8bd436d994883a6f8e8441308d3e/index.yaml
Debug[196768] in plugin 'helm-git': Trying to intercept for https://github.com/lucasfcnunes/wazuh-helm#v0.0.1
Debug[196768] in plugin 'helm-git': HELM_GIT_REPO_CACHE:~/.cache/helm/git-helm/repo is not a directory, cannot cache
/home/vscode/.local/share/helm/plugins/helm-git/helm-git: 154: cd: can't cd to ~/.cache/helm/git-helm/chart/759d8bd436d994883a6f8e8441308d3e
Error: open /tmp/helm-git.G3xsBB/~/.cache/helm/git-helm/chart/759d8bd436d994883a6f8e8441308d3e/index.yaml3973845737: no such file or directory
Error in plugin 'helm-git': Error while helm_index
Error: looks like "git+https://github.com/lucasfcnunes/wazuh-helm@?ref=v0.0.1" is not a valid chart repository or cannot be reached: plugin "helm-git" exited with error

The expected behavior

Should create the set folders in the env vars and cache the repo and chart in the respective path.

[aslafy-z]

I don't think it's a bug but a missing feature. I confirm helm-git does not create cache directories if they don't exists as of today. I would be happy to merge such a feature. PRs are welcome :)