fix: [M3-8630] - Add default root hostname for TXT records

[jaalah-akamai]

Description 📝

For A/AAA records we default to the root hostname if left empty or by using @, but we do not do the same for TXT record hostnames. Due to this discrepancy, there has been confusion to whether a TXT record for their root domain was applying correctly, or whether the A/AAAA records they were creating would apply to something like example.com.example.com.

Changes 🔄

• TXT has been added as a case in the shouldResolve function
• TXT hostname now defaults to root domain hostname

Target release date 🗓️

N/A

Preview 📷

good.mov

How to test 🧪

Reproduction steps

• Create domain in cloud manager
• Add an A record for that domain leaving the hostname field blank or using @
• Create a TXT record for that domain leaving the hostname field blank or using @
• Notice the difference in "hostname" column after those records have been saved.
  • The "hostname" column for A/AAAA/MX records reflects the root domain, while the hostname column for TXT records remains blank.

Verification steps

• Checkout branch or view preview link
• Observe TXT hostname populated accordingly.

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