[PLAT-15943] Yba Installer symlinking to be idempotent

Summary:
We found that the symlink function in yba-installer does not handle
the case where the symlink was already created. A new symlink in this
scenario leads to a file system loop.

We now detect when the symlink already exists, and delete and recreate it
if it does.

If the target file exists and is not a symlink, we should fail, as this
is an unexpected scenario

Test Plan: tested new symlink function during migration`

Reviewers: muthu, sanketh

Reviewed By: muthu

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D39748

managed/yba-installer/pkg/common/utils.go

@@ -175,6 +175,15 @@ func CreateSymlink(pkgDir string, linkDir string, binary string) error {
 
 // Symlink implements a more generic symlink utility.
 func Symlink(src string, dest string) error {
+	if stat, err := os.Lstat(dest); err == nil {
+		if stat.Mode()&os.ModeSymlink == 0 {
+			return fmt.Errorf("destination symlink '%s' already exists and is not a symlink", dest)
+		}
+		log.Debug("Deleting existing symlink at " + dest)
+		if err := os.Remove(dest); err != nil {
+			return fmt.Errorf("failed to delete symlink '%s': %w", dest, err)
+		}
+	}
 	out := shell.Run("ln", "-sf", src, dest)
 	out.SucceededOrLog()
 	return out.Error