infra: release script, validate proper ICEBERG_VERSION variable (#1956)

## Which issue does this PR close?

- Closes #.

## What changes are included in this PR?
Add a check that the input `ICEBERG_VERSION` variable is in the proper
format, i.e. `0.8.0`. Otherwise, the source directory and zip file will
have the wrong name

## Are these changes tested?


Added these 3 lines:
```
echo "Release version: $release_version"
echo "Git branch: $git_branch"
echo "Source directory: apache-iceberg-rust-$release_version"
```

This PR:
```
➜  iceberg-rust git:(kevinjqliu/validate-version) ✗ ICEBERG_VERSION=rc.1 ./scripts/release.sh  
var is set to 'rc.1'
Error: ICEBERG_VERSION (rc.1) must be in the format: <number>.<number>.<number>
➜  iceberg-rust git:(kevinjqliu/validate-version) ✗ ICEBERG_VERSION=0.8.0 ./scripts/release.sh 
var is set to '0.8.0'
Release version: 0.8.0
Git branch: release-0.8.0-rc.1
Source directory: apache-iceberg-rust-0.8.0
```

main:
```
➜  iceberg-rust git:(kevinjqliu/validate-version) ✗ ICEBERG_VERSION=rc.1 ./scripts/release.sh 
var is set to 'rc.1'
Release version: rc.1
Git branch: release-rc.1-rc.1
Source directory: apache-iceberg-rust-rc.1
➜  iceberg-rust git:(kevinjqliu/validate-version) ✗ ICEBERG_VERSION=0.8.0 ./scripts/release.sh
var is set to '0.8.0'
Release version: 0.8.0
Git branch: release-0.8.0-rc.1
Source directory: apache-iceberg-rust-0.8.0
```

Author: kevinjqliu

scripts/release.sh

@@ -25,6 +25,12 @@ else
 	echo "var is set to '$ICEBERG_VERSION'"
 fi
 
+# Validate version format (e.g., 1.0.0)
+if [[ ! "$ICEBERG_VERSION" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+	echo "Error: ICEBERG_VERSION ($ICEBERG_VERSION) must be in the format: <number>.<number>.<number>"
+	exit 1
+fi
+
 # tar source code
 release_version=${ICEBERG_VERSION}
 # rc versions