[MM-20979] Add first implementation of the Bleve search engine (#14562)

* [MM-20979] Add first implementation of the Bleve search engine

* Fix i18n

* Migrate searchengine utils tests

* Fix linter

* Don't add allTermsQ if both termQueries and notTermQueries are empty

* Fix test that should work if user is system admin

* Modify naming according to review comments

* Abstract getIndexDir function

* Extracting bleve engine name as a constant

* Merge both Indexer interfaces into one

* Add worker stopped message

* Allow worker to be started/stopped with config change

* Use constants for index names

* Modify test order

* Fix linter

* Trying to unlock the CI

vendor/github.com/couchbase/vellum/go.mod

@@ -0,0 +1,10 @@
+module github.com/couchbase/vellum
+
+go 1.12
+
+require (
+	github.com/blevesearch/mmap-go v1.0.2
+	github.com/spf13/cobra v0.0.5
+	github.com/willf/bitset v1.1.10
+	golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a // indirect
+)