Add Ecosia as search engine

[cndouglas]

Here are some comments in favor:

• Provide a lot more search engines for default search engine preference #1103 (comment)
• Modify search engine and some other features #5065 (comment)
• Add Yandex to search engine prefs and results #2703 (comment)
• https://community.brave.com/t/add-ecosia-search/1072
• Modify search engine and some other features #5065 (comment)

Q/A steps:

1. Open Preferences.
2. Open the Search section and select Ecosia from the list.
3. Turn on Autocomplete search term as you type if needed.
4. Activate the URLbar and type something (e.g. Brave).
5. Make sure the search suggestions appear in the autocomplete panel.
6. Press Enter.
7. Make sure the Ecosia search page appears with the specified search term(s).
8. Activate the URLbar and try the engine go key :e.