Add a reference for available config keys in help & docs

[Gedochao]

Fixes #1623

These changes add the available config keys to the config sub-command's --help and --full-help output (and thus, to the reference docs).
Only non-hidden (important for the average user) keys are listed in the short --help.

I also tweaked the config sub-command doc:

• it will now be in the main commands website level
• it's no longer a power command, so I fixed it not to be tagged as such

Short config help output:

scala-cli config -h
# Usage: scala-cli config [options]
# Configure global settings for Scala CLI.
# 
# Available keys:
#   actions                                        Globally enables actionable diagnostics. Enabled by default.
#   interactive                                    Globally enables interactive mode (the '--interactive' flag).
#   power                                          Globally enables power mode (the '--power' launcher flag).
#   suppress-warning.directives-in-multiple-files  Globally suppresses warnings about directives declared in multiple source files.
#   suppress-warning.outdated-dependencies-files   Globally suppresses warnings about outdated dependencies.
# 
# You are currently viewing the basic help for the config sub-command. You can view the full help by running: 
#    scala-cli config --help-full
# For detailed documentation refer to our website: https://scala-cli.virtuslab.org/docs/commands/misc/config
# 
# Config options:
#   --unset, --remove  Remove an entry from config

Full config help output:

scala-cli config --full-help
# Usage: scala-cli config [options]
# Configure global settings for Scala CLI.
# 
# Syntax:
#   scala-cli config key value
# For example, to globally set the interactive mode:
#   scala-cli config interactive true
#   
# Available keys:
#   actions                                        Globally enables actionable diagnostics. Enabled by default.
#   github.token                                   (hidden) GitHub token.
#   httpProxy.address                              (hidden) HTTP proxy address.
#   httpProxy.password                             (hidden) HTTP proxy password (used for authentication).
#   httpProxy.user                                 (hidden) HTTP proxy user (used for authentication).
#   interactive                                    Globally enables interactive mode (the '--interactive' flag).
#   interactive-was-suggested                      (hidden) Setting indicating if the global interactive mode was already suggested.
#   pgp.public-key                                 (hidden) The PGP public key, used for signing.
#   pgp.secret-key                                 (hidden) The PGP secret key, used for signing.
#   pgp.secret-key-password                        (hidden) The PGP secret key password, used for signing.
#   power                                          Globally enables power mode (the '--power' launcher flag).
#   publish.credentials                            (hidden) Publishing credentials, syntax: s1.oss.sonatype.org value:user value:password
#   publish.user.email                             (hidden) The 'email' user detail, used for publishing.
#   publish.user.name                              (hidden) The 'name' user detail, used for publishing.
#   publish.user.url                               (hidden) The 'url' user detail, used for publishing.
#   repositories.credentials                       (hidden) Repository credentials, syntax: value:user value:password
#   repositories.default                           (hidden) Default repository, syntax: https://first-repo.company.com https://second-repo.company.com
#   repositories.mirrors                           (hidden) Repository mirrors, syntax: repositories.mirrors maven:*=https://repository.company.com/maven
#   suppress-warning.directives-in-multiple-files  Globally suppresses warnings about directives declared in multiple source files.
#   suppress-warning.outdated-dependencies-files   Globally suppresses warnings about outdated dependencies.
# 
# For detailed documentation refer to our website: https://scala-cli.virtuslab.org/docs/commands/misc/config
# 
# Config options:
#   --dump             (hidden) Dump config DB as JSON
#   --unset, --remove  Remove an entry from config
#  (...)

[lwronski]

LGTM