Add Nile Delta map (#3306)

## Description:
Add Nile Delta as a new regional map. Features 11 nations across the
delta region (Alexandria, Damietta, Faraskur, Sheremsah, El
Senbellawein, Aga, Mit Ghamr, Cairo, Heliopolis, Memphis, El Mansoura).
1.36M land tiles at 1556x1280, terrain generated from real relief data.
Includes the Suez Canal. Playlist frequency: 4.

![Nile Delta
thumbnail](https://raw.githubusercontent.com/gabigabogabu/OpenFrontIO/feature/nile-delta-map/resources/maps/niledelta/thumbnail.webp)

## Checklist
- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

Source: https://commons.wikimedia.org/wiki/File:Niledelta_33.svg
Discord: gabigabogabu

CREDITS.md

@@ -49,6 +49,11 @@ Copyright © opentopography.org. All Rights Reserved. [Terms of Use](https://ope
 [USA Hawaii relief location map](https://commons.wikimedia.org/wiki/File:USA_Hawaii_relief_location_map.svg) by NordNordWest
 Licensed under [CC BY-SA 3.0 DE](https://creativecommons.org/licenses/by-sa/3.0/de/deed.en)
 
+### Nile Delta Map
+
+[Niledelta 33](https://commons.wikimedia.org/wiki/File:Niledelta_33.svg) by John187
+Licensed under [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)
+
 ## Icons
 
 ### [The Noun Project](https://thenounproject.com/)