Upgrade Solr from 9.2.1 to 9.4.0

[m-i-l]

Mostly just to keep up-to-date with the latest version, but there are some vector search related new features in 9.3.0 which might prove useful: https://solr.apache.org/docs/9_4_0/changes/Changes.html#v9.3.0.new_features

[m-i-l]

Relatively straightforward upgrade, but Solr issue referenced in #85 is still open so had to make the following find and replace in schema.xml:

filter name="stop" -> filter class="solr.StopFilterFactory"
filter name="lowercase" -> filter class="solr.LowerCaseFilterFactory"
filter name="synonymGraph" -> filter class="solr.SynonymGraphFilterFactory"
filter name="flattenGraph" -> filter class="solr.FlattenGraphFilterFactory"
filter name="keywordMarker" -> filter class="solr.KeywordMarkerFilterFactory"
filter name="englishPossessive" -> filter class="solr.EnglishPossessiveFilterFactory"
filter name="englishMinimalStem" -> filter class="solr.EnglishMinimalStemFilterFactory"
filter name="porterStem" -> filter class="solr.PorterStemFilterFactory"
filter name="wordDelimiterGraph" -> filter class="solr.WordDelimiterGraphFilterFactory"
filter name="removeDuplicates" -> filter class="solr.RemoveDuplicatesTokenFilterFactory"
filter name="reversedWildcard" -> filter class="solr.ReversedWildcardFilterFactory"
filter name="doubleMetaphone" -> filter class="solr.DoubleMetaphoneFilterFactory"
filter name="delimitedPayload" -> filter class="solr.DelimitedPayloadTokenFilterFactory"