fix(docs): mention --filter in all subcommand help

[pbrisbin]

optparse-applicative offers a header or a footer info modifier, but
they both put the text in the wrong place: either above or below
everything. To get the text to appear after the one-line description,
but before the options, we need to manually append it.

Here is the updated help,

% stackctl deploy --help
Usage: stackctl deploy [-p|--parameter KEY=[VALUE]] [-t|--tag KEY=[VALUE]]
                       [--save-change-sets DIRECTORY] [--no-confirm]
                       [--no-remove] [--clean]

  Deploy specifications

  By default, this will operate on the entire stack collection. To operate on a
  specific stack or set of stacks, use the --filter argument to filter the
  collection by file path.

Available options:
  -p,--parameter KEY=[VALUE]
                           Override the given Parameter for this operation
  -t,--tag KEY=[VALUE]     Override the given Tag for this operation
  --save-change-sets DIRECTORY
                           Save executed changesets to DIRECTORY
  --no-confirm             Don't confirm changes before executing
  --no-remove              Don't delete removed Stacks
  --clean                  Remove all changesets from Stack after deploy
  -h,--help                Show this help text

Global options:
  -d,--directory PATH      Use the stack collection located at PATH (default:
                           current working directory)
  --filter PATTERN[,PATTERN]
                           Filter specifications to match PATTERN(s)
  --color auto|always|never
                           When to colorize output
  -v,--verbose             Increase verbosity (can be passed multiple times)
  --auto-sso WHEN          Automatically run aws-sso-login if necessary?

NOTE: fullDescr was removed because it is the default.
helpShowGlobals was added because it was an oversight to not have it
before.