Handle metadata more elegantly

[albertmeronyo]

Currently we are just catching (thanks @c-martinez ) errors when we fail to parse query metadata. These are situations in which the parsing will most probably fail:

• Empty line at the beginning of the metadata section
• More than one empty line at the end of the metadata section
• Inconsistent indenting
• Etc.
  At the moment the backend fails silently, and simply no OpenAPI spec is rendered for the offending query metadata. Using the UI to at least show some error (and suggestions for fixing) would be a great addition