Fix successful temperature notification

[yubiuser]

What does this PR aim to accomplish?:

PR #2516 changes the way how we handle the temperature unit. After setting it via web interface it will show a success message. However, this notification is blue instead of the usual green

This PR fixed the color and adds a small success icon.

How does this PR accomplish the above?:

utils.showAlert expects an info type message first and a success/error afterwars. Only if info has been generated, it will change the style to subsequent messages.

https://github.com/pi-hole/AdminLTE/blob/b29a423b9553654f113bcdc8a82296eb6e4613d7/scripts/pi-hole/js/utils.js#L75-L76

This PR adds a info message (it will be barely seen, because it is replaced instantly with the success message).

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)
6. I have checked that another pull request for this purpose does not exist.
7. I have considered, and confirmed that this submission will be valuable to others.
8. I accept that this submission may not be used, and the pull request closed at the will of the maintainer.
9. I give this submission freely, and claim no ownership to its content.

---

• I have read the above and my PR is ready for review. Check this box to confirm

[rdwebdesign]

Note:
This PR also fix the error message, setting the alert to red in case of failure.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-22-web-v5-19-and-core-v5-16-1-released/61999/1