[bitnami/grafana-loki] Support alloy extraConfig

[Ayowel]

Description of the change

This adds support for .Values.grafanaalloy.alloy.extraConfig in the chart's secret file as would be expected when reading the README.

Benefits

Allow users to customize their grafana-alloy as would be expected from the README

Possible drawbacks

Users that have needlessly configured an extraConfig value might be surprised (as it is not used at the moment unless the grafana-alloy subchart's secret is used - in which case this chart's secret is unused), however this is a case of excess/useless configuration that should be safe to ignore.

Checklist

• Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• Title of the pull request follows this pattern [bitnami/<name_of_the_chart>] Descriptive title
• All commits signed off and in agreement of Developer Certificate of Origin (DCO)

[juan131]

Thanks so much for this contribution! Please check my comments

[juan131]

LGTM