fix: Allow filename starting with "http(s)://" while keeping an URL checking

[dduportal]

This PR ensures that the plugins "file" and "yaml" are able to read/write files which names starts with http:// or even https://, while keeping the auto-detection of URL location vs. file path.

• A new core package is added, named text, to treat all the read, write, diff, etc. operations outside the plugins (so that the 2 plugins does not depend on each other)

  • A new "ReadLine" method is added to allow extracting only a line from a text file (either URL or file) without loading it all on memory

• The method isURL (migrated in the text package):

  • Is used everywhere a hasprefix checking for http / https is used
  • checks if the file exists before trying to URL parse