`doctl databases firewalls append` removes descriptions for existing rules

**Describe the Issue:**
When using `doctl databases firewalls append` existing rules have their descriptions removed.

Repro:
1. Create a Postgres database cluster
2. Add a rule in the Network Access tab with a description.
3. use `doctl databases firewalls append --rule ip_addr:`
4. Refresh the Network Access tab for the database cluster
5. Description added for the rule created in step 2 is now empty.

**Environment:**

- doctl version: doctl version 1.163.0-release
- OS: Archlinux
- Installation method: package manager, pacman

Start at the `doctl databases firewalls append` command and reproduce the issue against a Postgres database cluster using the listed five-step sequence. Verify that appending a rule leaves the existing rule description unchanged; the work is done when that behavior is covered and confirmed with the command’s tests.

Written by the indexing model from the issue text.