add autocomplete for authors search

[dnoneill]

closes #4879

uses the default blacklight autocomplete and disables autocomplete by removing the src attribute when the dropdown isn't authors.

https://github.com/sul-dlss/sul-solr-configs/pull/368 needs to be merged as well

[cbeer]

Is this behind a feature flag? If not, can we do that so we can deploy this for testing without a long-lived branch.

[dnoneill]

@cbeer now has a feature flag

[cbeer]

the spell-check index won't be populated until after the weekend, but I'm seeing some odd matches..

for pou, it's suggesting:

"pou":{
        "numFound":5,
        "suggestions":[{
            "term":"puccini, giacomo, 1858-1924",
            "weight":34,
            "payload":""},
          {
            "term":"poulenc, francis, 1899-1963",
            "weight":10,
            "payload":""},
          {
            "term":"purcell, henry, 1659-1695",
            "weight":10,
            "payload":""},
          {
            "term":"ponchielli, amilcare, 1834-1886",
            "weight":8,
            "payload":""},
          {
            "term":"popp, lucia",
            "weight":7,
            "payload":""}]}

[dnoneill]

@cbeer That makes sense to me. I think solr suggest has stemming for such short queries. We could probably update it to do exact for 2-3 length queries, but if you look at earthworks that is also how it works.