CLI option output not consistent with other Canonical CLI utilities

Juju's help output has a different look and feel from other utilities produced by Canonical. In particular, the options (flags in Go parlance) have the following characteristics:

- no indent at the start of the line
- description is on the next line
- defaults appear next to the option, rather than after the usage instructions

Some examples:

$ juju help sla
[..,]

Global Options:
--debug (= false)
    equivalent to --show-log --logging-config=<root>=DEBUG
-h, --help (= false)
    Show help on a command or other topic.
--logging-config (= "")
    specify log levels for modules
--quiet (= false)
    show no informational output
--show-log (= false)
    if set, write the log file to stderr
--verbose (= false)
    show more verbose output

Command Options:
-B, --no-browser-login (= false)
    Do not use web browser for authentication
--budget (= "")
    the maximum spend for the model
--format (= tabular)
    Specify output format (json|tabular|yaml)
-m, --model (= "")
    Model to operate in. Accepts [<controller name>:]<model name>|<model UUID>
-o, --output (= "")
    Specify an output file

$ multipass help info
[...]

Options:
  -h, --help Display this help
  -v, --verbose Increase logging verbosity, repeat up to three times for
                     more detail
  --all Display info for all instances
  --format <format> Output info in the requested format.
                     Valid formats are: table (default), json, csv and yaml

LXC vertically aligns the long option forms of every command, even those without a short form. This provides the impression that each option is widely indented. Unlike the other commands, it uses the term flag rather than option.

$ lxc help info
[...]
Flags:
      --resources Show the resources available to the server
      --show-log Show the instance's last 100 log lines?
      --target Cluster member name

Global Flags:
      --debug Show all debug messages
      --force-local Force using the local unix socket
  -h, --help Print help
      --project string Override the source project
  -q, --quiet Don't show progress information
  -v, --verbose Show all information messages
      --version Print version number

$ snapcraft help login
[...]

Options:
  --with <login file> Path to file created with 'snapcraft export-login'
  -h, --help Show this message and exit.

The snap command is slightly different, using a leading tab and square brackets for its section headers, but retains the usage on the same line.

$ snap help find
[...]

[find command options]
      --private Search private snaps.
      --narrow Only search for snaps in “stable”.
      --section= Restrict the search to a given section.
      --color=[auto|never|always] Use a little bit of colour to highlight some things. (default: auto)
      --unicode=[auto|never|always] Use a little bit of Unicode to improve legibility. (default: auto)