[stable/mariadb] Add volume subPath for master

[gouglhupf]

What this PR does / why we need it:

Then specifying a existingClaim for the master it would be useful to be able to change the subPath within the existingClaim. This PR adds the option to add a subPath for the master's volume mount.

Which issue this PR fixes

To my knowledge there is no issue for this.

Special notes for your reviewer:

None

Checklist

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md
• Title of the PR starts with chart name (e.g. [stable/chart])

[k8s-ci-robot]

Hi @gouglhupf. Thanks for your PR.

I'm waiting for a helm member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[tompizmor]

/ok-to-test
/lgtm

[tompizmor]

/retest

[tompizmor]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gouglhupf, tompizmor

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