Make idle interval when clearing nlp cache configurable

modules/joex/src/main/resources/reference.conf

@@ -276,6 +276,13 @@ docspell.joex {
     # files.
     working-dir = ${java.io.tmpdir}"/docspell-analysis"
 
+    # The StanfordCoreNLP library caches language models which
+    # requires quite some amount of memory. Setting this interval to a
+    # positive duration, the cache is cleared after this amount of
+    # idle time. Set it to 0 to disable it if you have enough memory,
+    # processing will be faster.
+    clear-stanford-nlp-interval = "15 minutes"
+
     regex-ner {
       # Whether to enable custom NER annotation. This uses the address
       # book of a collective as input for NER tagging (to automatically

modules/joex/src/main/scala/docspell/joex/Config.scala

@@ -60,6 +60,7 @@ object Config {
   case class TextAnalysis(
       maxLength: Int,
       workingDir: Path,
+      clearStanfordNlpInterval: Duration,
       regexNer: RegexNer,
       classification: Classification
   ) {
@@ -67,6 +68,7 @@ object Config {
     def textAnalysisConfig: TextAnalysisConfig =
       TextAnalysisConfig(
         maxLength,
+        clearStanfordNlpInterval,
         TextClassifierConfig(
           workingDir,
           NonEmptyList