feat(crd/aws) TXT Record Support via DNSEndpoints

[onelapahead]

What would you like to be added:

Complimentary to #5741 - we would like the standard AWS Route53 provider to officially support TXT records management via the CRD source.

Why is this needed:

AWS Route53 is one of the most widely used providers of ExternalDNS for private and public DNS records. The ability to declaratively manage TXT records for internal or external discovery protocols, such as Ethereum's EIP-1459 would be very advantageous for users and Kubernetes operators alike.

Building off of #5740 - when testing the AWS provider with the CRD source for TXT records, a few bugs were encountered which prevented it from working as expected. Some of which is due to ExternalDNS's own use of TXT records for registries - and so support for managed TXT records has to be done with care to prevent introducing regressions involving the registry records.

Those bugs preventing this from working will be documented in comments below, and addressed in individual PRs. This feature can be consider completed once: the AWS provider can create/update/delete TXT records which contain arbitrary text and may have multiple targets i.e. strings defined within the CRD.

Hopefully, once this issue and #5741 are closed, support for other common providers such as Google Cloud, Azure, Alibaba, CloudFlare, and so on gets easier to implement or is inadvertently completed.

[onelapahead]

Related issues and PRs:

• Escaped double quotes of target prevents creation of TXT, NAPTR and CAA records with DNSEndpoint #3979
• Cannot create TXT records (AWS Zones) #4792
• Fixing NAPTR support #4212

Similar to NAPTR records, TXT records can contain arbitrary text, including ending with ., and so they must also be omitted from that check (see https://github.com/kubernetes-sigs/external-dns/pull/5740/files#diff-4d584eedf230b073e982a93ee4dc7fe2039aea6ca6c801872e30da86352bb4ecR260-R266 and https://github.com/kubernetes-sigs/external-dns/pull/5740/files#diff-c02e07605d186acb5c44104c288e87eb977562464aed0e870461f5b5393489e0R192-R195).

And then, when creating TXT records via DNSEndpoints its intuitive for the user to put:

  targets:
    - sometext

(in fact the docs say to do so). But if a user does this, AWS Route53 will complain the text isn't wrapped in quotes.

For registry TXT records, ExternalDNS internally handles this, but for TXT record targets via CRD source, it does not automatically do this. For other providers they might not mind, so we need to see wrap the TXT records in quotes if they aren't already before sending them to AWS APIs (see https://github.com/onelapahead/external-dns/pull/1/files#diff-95fde44621b48d924a9ad43138223f86d3012e63c65400f7051b7cad08096052R945-R954).