Change username validation message
What does this MR do and why?
Validation message has been changed from:
Username must not start or end with a special character and must not contain consecutive special characters.
to:
Username can only include letters, digits, '_', '-' and '.'. It must not start with '-', end in '.', '.git', or '.atom'. Avoid using accented characters or symbols.
These changes will affect the following areas that uses oci_repository_path_regex_message:
Related to #429283 (closed)