Use ocrmypdf tool to create pdf/a during conversion

- Use another external tool to convert pdf to pdf which also adds the
  extracted text as another layer into the pdf

- Although not used, the external conversion routine will now check
  for an existing text file that is named as the pdf file with extension
  `.txt`. If present it is included in the conversion result and will be
  used as the extracted text.

- text extraction for pdf files happens now on the converted file,
  because it may already contain the text from the conversion step and
  thus avoids running OCR twice.

- All errors during conversion are not fatal; processing continues
  without a converted file.

modules/store/src/main/scala/docspell/store/records/RFileMeta.scala

@@ -3,8 +3,10 @@ package docspell.store.records
 import docspell.common._
 import docspell.store.impl.Implicits._
 import docspell.store.impl._
+import docspell.store.syntax.MimeTypes._
 
 import bitpeace.FileMeta
+import bitpeace.Mimetype
 import doobie._
 import doobie.implicits._
 
@@ -30,4 +32,13 @@ object RFileMeta {
 
     selectSimple(Columns.all, table, Columns.id.is(fid)).query[FileMeta].option
   }
+
+  def findMime(fid: Ident): ConnectionIO[Option[MimeType]] = {
+    import bitpeace.sql._
+
+    selectSimple(Seq(Columns.mimetype), table, Columns.id.is(fid))
+      .query[Mimetype]
+      .option
+      .map(_.map(_.toLocal))
+  }
 }