Scripting: add support for fine-grained settings

Allow to on/off scripting based on their source (where they get loaded from), the  operation that executes them and their language.

The settings cover the following combinations:

- mode: on, off, sandbox
- source: indexed, dynamic, file
- engine: groovy, expressions, mustache, etc
- operation: update, search, aggs, mapping

The following settings are supported for every engine:

script.engine.groovy.indexed.update:    sandbox/on/off
script.engine.groovy.indexed.search:    sandbox/on/off
script.engine.groovy.indexed.aggs:      sandbox/on/off
script.engine.groovy.indexed.mapping:   sandbox/on/off
script.engine.groovy.dynamic.update:    sandbox/on/off
script.engine.groovy.dynamic.search:    sandbox/on/off
script.engine.groovy.dynamic.aggs:      sandbox/on/off
script.engine.groovy.dynamic.mapping:   sandbox/on/off
script.engine.groovy.file.update:       sandbox/on/off
script.engine.groovy.file.search:       sandbox/on/off
script.engine.groovy.file.aggs:         sandbox/on/off
script.engine.groovy.file.mapping:      sandbox/on/off

For ease of use, the following more generic settings are supported too:

script.indexed: sandbox/on/off
script.dynamic: sandbox/on/off
script.file:    sandbox/on/off

script.update:  sandbox/on/off
script.search:  sandbox/on/off
script.aggs:    sandbox/on/off
script.mapping: sandbox/on/off

These will be used to calculate the more specific settings, using the stricter setting of each combination. Operation based settings have precedence over conflicting source based ones.

Note that the `mustache` engine is affected by generic settings applied to any language, while native scripts aren't as they are static by definition.

Also, the previous `script.disable_dynamic` setting can now be deprecated.

Closes #6418
Closes #10116
Closes #10274

dev-tools/create-bwc-index.py

@@ -135,7 +135,8 @@ def start_node(version, release_dir, data_dir, tcp_port, http_port):
     '-Des.cluster.name=bwc_index_' + version,  
     '-Des.network.host=localhost', 
     '-Des.discovery.zen.ping.multicast.enabled=false',
-    '-Des.script.disable_dynamic=true',
+    '-Des.script.inline=on',
+    '-Des.script.indexed=on',
     '-Des.transport.tcp.port=%s' % tcp_port,
     '-Des.http.port=%s' % http_port
   ]