Suppress illegal access in plugin install (#41620)

We use Bouncy Castle to verify signatures when installing official
plugins. This leads to illegal access warnings because Bouncy Castle
accesses the Sun security provider constructor. This commit adds an
add-opens flag to suppress this illegal access.

distribution/src/bin/elasticsearch-plugin

@@ -1,6 +1,7 @@
 #!/bin/bash
 
-ES_MAIN_CLASS=org.elasticsearch.plugins.PluginCli \
+ES_JAVA_OPTS="--add-opens java.base/sun.security.provider=ALL-UNNAMED $ES_JAVA_OPTS" \
+  ES_MAIN_CLASS=org.elasticsearch.plugins.PluginCli \
   ES_ADDITIONAL_CLASSPATH_DIRECTORIES=lib/tools/plugin-cli \
   "`dirname "$0"`"/elasticsearch-cli \
   "$@"