chore(release): update GitHub workflow and Helm config

[electrosenpai]

Description

This pull request introduces several changes to the GitHub Action workflow:

• Change of release files location: The release files are now stored in the artifacts/ directory instead of charts/. This prevents conflicts when creating Helm packages due to dependencies within Helm.

• Added default values for apiUrl and frontUrl: Previously, if these values were commented out, Helm would ignore them, causing the following error:

$ helm template my-lago lago/lago --version 1.15.0 --set lago.apiUrl=https://api.domain.tld/ --set lago.frontUrl=https://app.domain.tld/ --debug install.go:218: [debug] Original chart version: "1.15.0" install.go:235: [debug] CHART PATH: /home/pb/.cache/helm/repository/lago-1.15.0.tgz

Error: execution error at (lago/templates/worker-deployment.yaml:68:24): apiUrl value is required helm.go:84: [debug] execution error at (lago/templates/worker-deployment.yaml:68:24): apiUrl value is required

This should fix issue #120

• Added Helm packages to .helmignore: Helm was previously including these packages inside new packages by default, which quickly inflated the package size. This led to the following error:

charts helm install my-lago lago2/lago --version 1.15.4 --values value_old.yaml
Error: INSTALLATION FAILED: create: failed to create: Request entity too large: limit is 3145728