[bitnami/grafana-loki] Allow disabling enableServiceLinks

[bpfoster]

Description of the change

Some other charts allow configuring whether service links are enabled or not. This PR will allow disabling service links individually on all the loki workloads. By default, service links are enabled, so there is no change to existing behavior.

Benefits

Users can disable service links. If they have a lot of workloads, there may be a lot of environment variables populated which are not used.

Possible drawbacks

None to my knowledge.

Applicable issues

Additional information

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)

[bpfoster]

I think the test failure here is unrelated. I randomly get a goss failure on both this commit and the one prior.

[alemorcuq]

Thanks!