Docs: Fix rendering of APIs that mention version (#41154)

Fixes rendering the `version_qualified` attribute in the docs. This
attribute includes `-SNAPSHOT` but does not include `-alpha` or `-beta`
and represents the `version` field as returned by `GET /` or
`GET /_cat/plugins`. Without this change we just drop the entire line on
the floor rather than render it so the output looks bad.

docs/Versions.asciidoc

@@ -1,4 +1,8 @@
 :version:               8.0.0-alpha1
+////
+bare_version never includes -alpha or -beta
+////
+:bare_version:          8.0.0
 :major-version:         8.x
 :prev-major-version:    7.x
 :lucene_version:        8.0.0
@@ -42,6 +46,7 @@ ifeval::["{release-state}"=="unreleased"]
 :percolator-client-javadoc: https://snapshots.elastic.co/javadoc/org/elasticsearch/plugin/percolator-client/{version}-SNAPSHOT
 :matrixstats-client-javadoc: https://snapshots.elastic.co/javadoc/org/elasticsearch/plugin/aggs-matrix-stats-client/{version}-SNAPSHOT
 :rank-eval-client-javadoc: https://snapshots.elastic.co/javadoc/org/elasticsearch/plugin/rank-eval-client/{version}-SNAPSHOT
+:version_qualified: {bare_version}-SNAPSHOT
 endif::[]
 
 ifeval::["{release-state}"!="unreleased"]
@@ -55,6 +60,7 @@ ifeval::["{release-state}"!="unreleased"]
 :percolator-client-javadoc: https://artifacts.elastic.co/javadoc/org/elasticsearch/plugin/percolator-client/{version}
 :matrixstats-client-javadoc: https://artifacts.elastic.co/javadoc/org/elasticsearch/plugin/aggs-matrix-stats-client/{version}
 :rank-eval-client-javadoc: https://artifacts.elastic.co/javadoc/org/elasticsearch/plugin/rank-eval-client/{version}
+:version_qualified: {bare_version}
 endif::[]
 
 :javadoc-client: {rest-high-level-client-javadoc}/org/elasticsearch/client