Prefixes with getUrl and Adapter::has() for directories

Fixes:

• normalizePath broken has() method for dir #11 - reported by @goffyara
• getUrl($path)` prints incorrect URL when prefix is defined in config #12 - reported by @taka-oyama

PHP 8, CanOverwriteFiles, GitHub actions

• Indicate that GCS adapter can overwrite file #13 - @daohoangson
• move to GitHub actions
• remove ScrutinizerCI
• code-style amendments
• effective support for PHP 8

v1.1.0

• allow using current google/cloud library