docs: rewrite the JSON connector page for the 15.9 implementation

[marevol]

The 15.9 JSON connector page still described a much older connector. Seven
parameters were missing entirely, and several statements the page did make are
no longer true. This rewrites it in all seven languages.

The page content was checked against the current fess-ds-json master by
running real data store crawls on a live Fess 15.9.0-SNAPSHOT, rather than by
reading the source alone.

Corrected

The page said	Actually
JSON Lines only; an array or a pretty-printed document "cannot be read directly, convert it to JSON Lines"	Three shapes are supported — JSON Lines, an array of objects, and a single object — and the shape is detected from the document by default
"If both are given, files takes priority and directories is ignored"	They are not exclusive. Both are processed, and a file reachable through both is read once
"The parameter name is the camelCase fileEncoding, not the snake_case file_encoding"	Both spellings resolve, for every parameter
Install to app/WEB-INF/lib	app/WEB-INF/plugin — where the admin UI installs plugins, and what the plugin README documents. (WEB-INF/lib also happens to be on the crawler child classpath, so it did work; it is just not the managed location.)
Download from Maven Central	Maven Central carries 15.7.0 and earlier. 15.8.0 onwards is published to the CodeLibs repository
Script examples in Groovy-only syntax (?:, as Float, collect {})	Fess 15.9 replaced the built-in engine with JavaScript and moved Groovy out to fess-script-groovy, so those no longer run under the default engine

Added

None of this was documented anywhere on the page before.

• The full parameter table: recursive, max_depth, include_pattern,
  exclude_pattern, file_suffixes, format and root_path in addition to
  the three that were already there.
• File discovery order — files in the order given, directory contents
  oldest first, files before directory contents; the suffix filter applies to
  files too.
• format — what auto decides, when jsonl is worth setting explicitly,
  and how the choice decides what a malformed record costs: one line in JSON
  Lines, potentially the rest of the source in the other shapes.
• root_path — array to N records, object to one, no match to none, the
  ~0/~1 escapes, and its precedence over format. A leading / is
  required; omitting it fails the whole data config without naming the
  parameter, so that gets a warning directive.
• Error routing — which parameter errors abort the crawl with a failure URL
  named after the parameter, and which are logged and defaulted.
• A note that a data store crawl finishes normally even when it indexed
  nothing, so the index count and the failure URLs are what to judge by.
• A note that the app.encrypt.property.pattern masking is a case-sensitive
  full match on the parameter name, so access_token is masked but
  accessToken is not.

Notes

• Only the 15.9 (development) tree is touched; earlier versions are left as
  they are.
• Every page parses cleanly under docutils.
• The Japanese page is the source; the other six follow it section for section
  and reuse each language's existing ds-csv.rst terminology.