SLT-1193: Frontend chart: Remove deprecated mailhog service from the chart

[k4lv15]

Changes proposed:

• Remove mailhog that was deprecated in SLT-1103: Frontend chart: Add support for mailpit, deprecate mailhog #141 and replaced by mailpit, clean up chart from mailhog's configuration.

How to test:

• See that chart validation and deployment is green: https://app.circleci.com/pipelines/github/wunderio/frontend-project-k8s?branch=feature%2FSLT-1193-rm-mail
• See that mailpit still works and is available under frontend's /mailpit path.

[Copilot]

Pull Request Overview

This PR removes the deprecated mailhog service configurations from the chart and associated files, ensuring that only mailpit remains for email handling.

• Removed mailhog configuration values and schema definitions from values.yaml and values.schema.json
• Deleted mailhog-specific logic in template files (varnish, configmap, checks, and helpers) and corresponding documentation in NOTES.txt
• Updated Chart.yaml and CI configuration to remove mailhog dependencies and repositories

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
charts/frontend/values.yaml	Removed mailhog configuration blocks
charts/frontend/values.schema.json	Removed mailhog schema definitions
charts/frontend/templates/varnish-configmap-vcl.yaml	Removed mailhog routing logic from varnish configuration
charts/frontend/templates/configmap.yaml	Removed mailhog location block and replaced it with mailpit redirection
charts/frontend/templates/checks.yaml	Removed mailhog validation checks
charts/frontend/templates/_helpers.tpl	Removed mailhog naming validations
charts/frontend/templates/NOTES.txt	Deleted mailhog documentation notes
charts/frontend/Chart.yaml	Removed mailhog dependency from chart metadata
.circleci/config.yml	Updated helm repository configurations to match the removal

Comments suppressed due to low confidence (1)

charts/frontend/templates/configmap.yaml:168

• It would be helpful to add an inline comment clarifying that the '/mailhog' location block now serves exclusively to redirect legacy traffic to mailpit, to assist future maintainers.

location /mailhog {

[k4lv15]

Postponed until mailhog is properly deprecated in #148, marking as draft for now.