Suggestion: Set intellij project icon (#5467)

Motivation:

There is no intellij project icon.

Modifications:

- Add icon to `.idea/icon.svg`
- (Copied and edited [this logo file](https://github.com/line/armeria/blob/main/site/src/design/armeria_icon.svg) to trim space and make square)

Result:

- Looks good

<img width="468" alt="Screenshot 2024-02-15 at 9 03 32 PM" src="https://github.com/line/armeria/assets/11611397/8a87e959-9009-469d-8262-10d23cf686ae">

example


<img width="1035" alt="Screenshot 2024-02-15 at 9 14 31 PM" src="https://github.com/line/armeria/assets/11611397/9aa4d105-6ee0-45c5-ad5a-68e6f6c30bdf">

Project icon can be set from welcome page

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.gitignore

@@ -28,7 +28,8 @@ hs_err_pid*
 .gradle
 
 # IntelliJ
-.idea
+**/.idea/*
+!.idea/icon.svg
 *.iml
 *.iws
 *.ipr