Handle the migration to the new TXT format: missing records to be created separately

[alebedev87]

Description
Follow-up of #2811. Aims at addressing the following error when the missing new format TXT record gets created and deleted in the same batch:

Applying provider record filter for domains: [external.dns. .external.dns.]"
time="2022-07-26T07:17:45Z" level=info msg="Desired change: UPSERT cname-externaldns-e2e.external.dns TXT [Id: /hostedzone/]"
time="2022-07-26T07:17:45Z" level=info msg="Desired change: UPSERT externaldns-e2e.external.dns A [Id: /hostedzone/]"
time="2022-07-26T07:17:45Z" level=info msg="Desired change: UPSERT externaldns-e2e.external.dns TXT [Id: /hostedzone/]"
time="2022-07-26T07:17:45Z" level=info msg="Desired change: CREATE cname-externaldns-e2e.external.dns TXT [Id: /hostedzone/]"
time="2022-07-26T07:17:46Z" level=error msg="Failure in zone external.dns. [Id: /hostedzone/]"
time="2022-07-26T07:17:46Z" level=error msg="InvalidChangeBatch: [The request contains an invalid set of changes for a resource record set 'TXT cname-externaldns-e2e.external.dns.']\n\tstatus code: 400, request id: "

This error may happen when the DNS record was created with the external-dns of version < 0.12.0 then the target of the source changed (ClusterIP, LoadBalancer's DNS record, HostIP) and then the new (> 0.12.0) version kicks the migration logic. The migration code sees that there is a new format TXT record is missing and adds it as "to be created" however the target changed and A/CNAME record needs to be changed too along with its TXT records.

Checklist

• Unit tests updated
• End user documentation updated

[alebedev87]

/assign @Raffo

[Raffo]

Thanks for this PR! I will build an image and test it. Can you add unit tests in the meantime?

[alebedev87]

@Raffo : added a test which checks that a new plan is applied in case there are missing records.

[Raffo]

I e2e tested this, LGTM

/approve
/lgtm

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