Improve metadata file validation

[mzur]

The current volume metadata file validation is performed in two steps. First, the format-specific validation is performed in recognizesFile(). Second, the validation of the parsed metadata is performed.

The first validation step is not implemented very well because a user uploading a malformed file only gets a message "file is not valid". We should implement a mechanism for metadata parsers to return more meaningful error messages for the validation (e.g. "category x is missing the name attribute"). The recognizesFile() method can be replaced with a validate() method that may return a special MetadataValidationException with a message that is passed on to the frontend. Any other exception is handled like an unexpected server error.

[mzur]

The validation is performed here:

• core/app/Http/Requests/StorePendingVolume.php

  Line 85 in 929fcb6

  if (!$parser->recognizesFile()) {

• core/app/Http/Requests/StoreVolume.php

  Line 119 in 929fcb6

  if (!$parser->recognizesFile()) {

• core/app/Http/Requests/StoreVolumeMetadata.php

  Line 79 in 929fcb6

  if (!$parser->recognizesFile()) {

The parsers implement it here:

• core/app/Services/MetadataParsing/MetadataParser.php

  Line 34 in 929fcb6

  abstract public function recognizesFile(): bool;

• core/app/Services/MetadataParsing/CsvParser.php

  Line 52 in 929fcb6

  public function recognizesFile(): bool

• https://github.com/biigle/metadata-ifdo/blob/da0ab36ddce12c402d9db0c9873c087c9a3b360d/src/IfdoParser.php#L43
• https://github.com/biigle/metadata-coco/blob/4b7da60a2e00acc8f88fd3360b8e1f7c0a697243/src/CocoParser.php#L48