[bitnami/keycloak] Add support for PEM certificates

[migruiz4]

Description of the change

Adds the value auth.tls.usePem that allows users to provide their certificates in PEM format by reusing the existing code for autoGenerated certs.

In addition, removes unused variables from configmap-env-vars.yaml

Benefits

An additional feature, supported by the upstream container: https://github.com/keycloak/keycloak-containers/blob/main/server/tools/x509.sh

Possible drawbacks

None known.

Applicable issues

• fixes keycloak add cacert value or better documentation using existing values #7536 (comment)

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md using (readme-generator-for-helm)[https://github.com/bitnami-labs/readme-generator-for-helm]
• Title of the PR starts with chart name (e.g. [bitnami/<name_of_the_chart>])
• All commits signed off and in agreement of Developer Certificate of Origin (DCO)