[OC11] Modify doc for files:scan --groups

[phil-davis]

owncloud/core#31719 proposes to modify the files:scan --groups option so that each of multiple groups are listed by specifying the option multiple times e.g.:

occ files:scan --group=foo --group=bar --group=a,b

This allows the sysadmin to scan a group that has a literal comma in its name - e.g. a,b

New help output is:

occ files:scan --help
Usage:
  files:scan [options] [--] [<user_id>]...

Arguments:
  user_id                Will rescan all files of the given user(s).

Options:
      --output[=OUTPUT]  The output format to use (plain, json or json_pretty, default is plain). [default: "plain"]
  -p, --path=PATH        Limit rescan to this path, e.g., --path="/alice/files/Music", the user_id is determined by the path and the user_id parameter and --all are ignored.
  -g, --group=GROUPS    Scan user(s) under the group(s). This option can be used as --group=foo --group=bar to scan groups foo and bar (multiple values allowed)
  -q, --quiet            Do not output any message
      --all              Will rescan all files of all known users.
      --repair           Will repair detached filecache entries (slow).
      --unscanned        Only scan files which are marked as not fully scanned.
  -h, --help             Display this help message
  -V, --version          Display this application version
      --ansi             Force ANSI output
      --no-ansi          Disable ANSI output
  -n, --no-interaction   Do not ask any interactive question
      --no-warnings      Skip global warnings, show command output only
  -v|vv|vvv, --verbose   Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug

Help:
  Scans the filesystem for changes and updates the file cache accordingly.

Update the doc, if the PR is merged.

[voroyam]

PR is still open, waiting for review of PR

[phil-davis]

PR owncloud/core#31719 was merged to core master 6 Aug 2018.
This issue can be documented and then wait until it is known when/what release it will go in.

[phil-davis]

PR #642 has the needed changes.

[phil-davis]

PR merged to master. It will get released in the "normal" workflow whenever the corresponding core master code is released.