Add proper indentation to extra CoreDNS config

[javipolo]

When using more than one line of extra config, the indentation was not right and generated YAML was not valid

This should fix this issue

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
To complete the pull request process, please assign c-knowles
You can assign the PR to them by writing /assign @c-knowles in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-io]

Codecov Report

Merging #1813 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1813   +/-   ##
======================================
  Coverage    24.6%   24.6%           
======================================
  Files          98      98           
  Lines        5069    5069           
======================================
  Hits         1247    1247           
  Misses       3682    3682           
  Partials      140     140

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3f0b254...74aae52. Read the comment docs.

[davidmccormick]

/lgtm

[davidmccormick]

Many thanks for this fix! 🙏