add search validate+explain (#31)

TODO.md

@@ -1,40 +1,13 @@
 - [Go client docs](https://www.elastic.co/docs/reference/elasticsearch/clients/go/typed-api)
 - [ES API docs](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-get)
 
-- Fix index names custom completion
-  https://github.com/urfave/cli/issues/2332
-  https://github.com/urfave/cli/issues/2333
-
 - index show: add more details, see screenshots
 
 - add shard explain, aka:
   get /_cluster/allocation/explain {"index":"yourindex", "primary": true, "shard":0}
 
 
-- add validate:
-
-> GET /mock/_validate/query?rewrite=true {"from":0,"query":{"bool":{"must":[{"match_all":{}}]}},"size":20,"sort":[{"name":{"order":"desc"}}]}
-{
-  "valid": false
-}
-
-- add explain to search (maybe option -e)
-
-> GET /mock/_explain/1780043878 {"query":{"bool":{"must":[{"match_all":{}}]}}}
-{
-  "_index": "mock",
-  "_id": "1780043878",
-  "matched": true,
-  "explanation": {
-    "value": 1.0,
-    "description": "*:*",
-    "details": []
-  }
-}
-
 - add datastream support:
   https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-indices-get-data-stream
   
   also exclude data stream backing indices from index ls
-  
-- add filter option to index ls (regex), maybe to other ls commands as well, use -F <filter>