helm: Don't suppress configuration for registries other than TXT

[johngmyers]

Description

The "aws-sd" and "dynamodb" registries also consume txtOwnerId. The "dynamodb" registry will also soon be consuming txtPrefix and txtSuffix.

Also document these existing settings.

Checklist

• Unit tests updated
• End user documentation updated

[mloiseleur]

@johngmyers Wdyt about changing also the help message of the CLI. Currently with --help:

  --txt-owner-id="default"       When using the TXT registry, a name that identifies this instance of ExternalDNS
                                 (default: default)

I suggest to replace it with something like

  --txt-owner-id="default"       When using the registry, a name that identifies this instance of ExternalDNS
                                 (default: default)

[johngmyers]

@mloiseleur chaging the description of the flag would be good, but is outside the scope of this PR.

I put a more complete description in the second paragraph of https://github.com/kubernetes-sigs/external-dns/blob/master/docs/registry/registry.md

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[stevehipwell]

Suggested change

	{{- if and (eq .Values.txtPrefix "") (ne .Values.txtSuffix "") }}
	{{- if and (not .Values.txtPrefix "") .Values.txtSuffix }}

This change would be worth making for consistency while modifying this area.

[stevehipwell]

Thanks for the PR @johngmyers, this looks good to me. I did add a single comment which is IMHO a worthwhile change but it's not necessary.

/approve

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This pull-request has been approved by: johngmyers, mloiseleur, stevehipwell

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