etherpad: update to v1.8.17

Following https://github.com/bigbluebutton/bigbluebutton/pull/14550 .

Also updated the settings.json file with https://github.com/ether/etherpad-lite/blob/1.8.17/settings.json.template .

Made sure to preserve BigBlueButton common settings and a couple of extras
that I imagine that made sense for the docker environment:

 - ip: 0.0.0.0
	BigBlueButton uses 127.0.0.1

  /*
   * IP and port which Etherpad should bind at.
   *
   * Binding to a Unix socket is also supported: just use an empty string for
   * the ip, and put the full path to the socket in the port parameter.
   *
   * EXAMPLE USING UNIX SOCKET:
   *    "ip": "",                             // <-- has to be an empty string
   *    "port" : "/somepath/etherpad.socket", // <-- path to a Unix socket
   */
  "ip": "0.0.0.0",
  "port": 9001,

 - host: redis
	BigBlueButton uses 127.0.0.1

  /*
   * The type of the database.
   *
   * You can choose between many DB drivers, for example: dirty, postgres,
   * sqlite, mysql.
   *
   * You shouldn't use "dirty" for for anything else than testing or
   * development.
   *
   *
   * Database specific settings are dependent on dbType, and go in dbSettings.
   * Remember that since Etherpad 1.6.0 you can also store this information in
   * credentials.json.
   *
   * For a complete list of the supported drivers, please refer to:
   * https://www.npmjs.com/package/ueberdb2
   */

  "dbType": "redis",
  "dbSettings": {
    "host": "redis",
    "port": 6379
  },

 - soffice: /etherpad-export.sh
	BigBlueButton uses /usr/share/bbb-libreoffice-conversion/etherpad-export.sh

  /*
   * This is the absolute path to the soffice executable.
   *
   * LibreOffice can be used in lieu of Abiword to export pads.
   * Setting it to null disables LibreOffice exporting.
   */
  "soffice": "/etherpad-export.sh",

 - disableIPlogging: true
	BigBlueButton uses false (Etherpad's default)

  /*
   * Privacy: disable IP logging
   */
  "disableIPlogging": true,

 - host: redis
	BigBlueButton uses 127.0.0.1

  /*
   * Redis publisher plugin configuration.
   * npm i git+https://git@github.com/mconf/ep_redis_publisher.git
   */

  "ep_redis_publisher": {
    "host": "redis",
    "port": 6379
  },

mod/etherpad/Dockerfile

@@ -1,4 +1,4 @@
-FROM etherpad/etherpad:1.8.16
+FROM etherpad/etherpad:1.8.17
 
 USER root