[bitnami/wordpress] Non-manual chart upgrades

[mamiu]

Description of the change

IMPORTANT: Only merge this PR once #9268 is merged.

Automatically get the correct wordpress password on wordpress chart upgrade.

Currently the following error message is shown when a user wants to upgrade the [bitnami/wordpress] helm chart without having specified an existingSecret or the wordpressPassword, mariadb.auth.password and mariadb.auth.rootPassword value:

Error: UPGRADE FAILED: template: wordpress/templates/NOTES.txt:108:4: executing "wordpress/templates/NOTES.txt" at <include "common.errors.upgrade.passwords.empty" (dict "validationErrors" $passwordValidationErrors "context" $)>:
error calling include: template: wordpress/charts/common/templates/_errors.tpl:21:48: executing "common.errors.upgrade.passwords.empty" at <fail>: error calling fail: HELM_ERR_START

PASSWORDS ERROR: You must provide your current passwords when upgrading the release.
                 Note that even after reinstallation, old credentials may be needed as they may be kept in persistent volume claims.
                 Further information can be obtained at https://docs.bitnami.com/general/how-to/troubleshoot-helm-chart-issues/#credential-errors-while-upgrading-chart-releases

    'mariadb.auth.rootPassword' must not be empty, please add '--set mariadb.auth.rootPassword=$MARIADB_ROOT_PASSWORD' to the command. To get the current value:

        export MARIADB_ROOT_PASSWORD=$(kubectl get secret --namespace "the-wp-namespace" wordpress-test-mariadb-prod -o jsonpath="{.data.mariadb-root-password}" | base64 --decode)

    'mariadb.auth.password' must not be empty, please add '--set mariadb.auth.password=$MARIADB_PASSWORD' to the command. To get the current value:

        export MARIADB_PASSWORD=$(kubectl get secret --namespace "the-wp-namespace" wordpress-test-mariadb-prod -o jsonpath="{.data.mariadb-password}" | base64 --decode)

Benefits

The upgrade won't fail and the user doesn't have to retrieve and specify the secrets manually.
This change allows the user to upgrade the chart without worrying.

Possible drawbacks

None.

Applicable issues

• similar to [bitnami/mariadb] Don't overwrite generated secret values on chart upgrade #7403

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
• 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)

[marcosbc]

Thanks for the PR @mamiu, since it is going to be hard for us to keep track of this PR after #9268 is merged, let us know to merge this PR.

[mamiu]

@marcosbc Sure thing, no worries! I'll let you know once #9268 is merged.

[mamiu]

@marcosbc PR #9268 is merged now. So this one is ready to be reviewed.

[marcosbc]

Thanks @mamiu! Could you fix the conflicts with the master branch? Apart from that, it LGTM!

[mamiu]

@marcosbc Thanks for the review! The conflicts are resolved now.

[marcosbc]

LGTM! Thanks!!!