The default mustache engine was using HTML escaping which breaks queries
if used with JSON etc. This commit adds escaping for:
```
\b Backspace (ascii code 08)
\f Form feed (ascii code 0C)
\n New line
\r Carriage return
\t Tab
\v Vertical tab
\" Double quote
\\ Backslash
```
Closes#5473
Adds support for storing mustache based query templates that can later be filled
with query parameter values at execution time. Templates may be both quoted,
non-quoted and referencing templates stored in config/scripts/*.mustache by file
name.
See docs/reference/query-dsl/queries/template-query.asciidoc for templating
examples.
Implementation detail: mustache itself is being shaded as it depends directly on
guava - so having it marked optional but included in the final distribution
raises chances of version conflicts downstream.
Fixes#4879
Simon Willnauer
Isabel Drost-Fromm