DEV-3175-new-go-exercise-printfirsthalf (#1348)

* add subject for localhost

* fix the name

* add hints && add conditions

* Update README.md

* add cgi condition

* add condition of http code and redirections

* Update README.md

* Localhost Subject

* feat: Update the audir

* feat: Update the audit

* Add bonus part

* Update README.md

* add condition in bonus part

* Update README.md

* Update README.md

* feat: subject

* feat: subject

* feat: subject of Printfirsthalf

* feat: subject of Printfirsthalf

* Update README.md

* feat: subject of Printfirsthalf

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Correct  a Typo

* Update README.md

* docs(printfirsthalf): fix subject

- fix exercise header
- upgrade instructions
- add missig import 'fmt'/'piscine'
- fix console
- fix white-spaces and indentation

* docs(printfirsthalf): instructions upgrade

* feat(go-checkpoints): add new exercise retainfirsthalf

the exercise has been renamed from printfirsthalf to retain first half

* docs(retainfirsthalf): directory name changed accordingly to new name

---------

Co-authored-by: hamza <hamzaelkhatri@gmail.com>
Co-authored-by: Hamza elkhatri <40549481+Hamzaelkhatri@users.noreply.github.com>
Co-authored-by: Tiago Collot <collot.tiago1@gmail.com>
Co-authored-by: Michele Sessa <mikysett@gmail.com>

subjects/retainfirsthalf/README.md

@@ -0,0 +1,47 @@
+## retainfirsthalf
+
+### Instructions
+
+Write a function called `RetainFirstHalf()` that takes a `string` as an argument and returns the first half of this `string`.
+
+- If the length of the `string` is odd, round it down.
+- If the `string` is empty, return an empty string.
+- If the `string` length is equal to one, return the string.
+
+### Expected function
+
+```go
+func RetainFirstHalf(str string) string {
+
+}
+```
+
+### Usage
+
+Here is a possible program to test your function:
+
+```go
+package main
+
+import (
+	"fmt"
+	"piscine"
+)
+
+func main() {
+	fmt.Println(solutions.RetainFirstHalf("This is the 1st halfThis is the 2nd half"))
+	fmt.Println(solutions.RetainFirstHalf("A"))
+	fmt.Println(solutions.RetainFirstHalf(""))
+	fmt.Println(solutions.RetainFirstHalf("Hello World"))
+}
+```
+
+And its output:
+
+```console
+$ go run . | cat -e
+This is the 1st half$
+A$
+$
+Hello$
+```