Prevent duplicate left joins in translation order queries.

[shaunluedeke]

This pull request modifies the scopeOrderByTranslation method in src/Translatable/Traits/Scopes.php to improve its functionality and flexibility by adding support for specifying a locale and optimizing the query logic.

Enhancements to scopeOrderByTranslation:

• Added an optional ?string $local = null parameter to allow specifying a locale directly when ordering translations. If not provided, the method defaults to using the current locale.
• Optimized the query logic by checking for existing LEFT JOIN clauses on the translations table before adding a new one, preventing redundant joins and improving query efficiency.
• Removed redundant variables ($localeKey and $keyName) and streamlined the join logic to use class methods directly for retrieving keys and table names.

[shaunluedeke]

fixes #193