[gh env] Introduce gh env list subcommand - #10423

# main help text entry for core commands
$ bin/gh help
Work seamlessly with GitHub from the command line.

USAGE
  gh <command> <subcommand> [flags]

CORE COMMANDS
  auth:        Authenticate gh and git with GitHub
  browse:      Open repositories, issues, pull requests, and more in the browser
  codespace:   Connect to and manage codespaces
  env:         Manage deployment environments
  gist:        Manage gists
  issue:       Manage issues
  org:         Manage organizations
  pr:          Manage pull requests
  project:     Work with GitHub Projects.
  release:     Manage releases
  repo:        Manage repositories
...

$ bin/gh help env
Work with GitHub deployment environments.

To learn more about GitHub deployment environments, see
<https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-deployments/managing-environments-for-deployment>.


USAGE
  gh env <command> [flags]

AVAILABLE COMMANDS
  list:        List GitHub deployment environments

FLAGS
  -R, --repo [HOST/]OWNER/REPO   Select another repository using the [HOST/]OWNER/REPO format

INHERITED FLAGS
  --help   Show help for command

EXAMPLES
  $ gh env list

LEARN MORE
  Use `gh <command> <subcommand> --help` for more information about a command.
  Read the manual at https://cli.github.com/manual
  Learn about exit codes using `gh help exit-codes`

$ bin/gh env list --help 
List GitHub deployment environments

For more information about output formatting flags, see `gh help formatting`.

USAGE
  gh env list [flags]

ALIASES
  gh env ls

FLAGS
  -q, --jq expression     Filter JSON output using a jq expression
      --json fields       Output JSON with the specified fields
  -L, --limit int         Maximum number of environments to fetch (default 30)
  -t, --template string   Format JSON output using a Go template; see "gh help formatting"
  -w, --web               Open environments in the browser

INHERITED FLAGS
      --help                     Show help for command
  -R, --repo [HOST/]OWNER/REPO   Select another repository using the [HOST/]OWNER/REPO format

JSON FIELDS
  canAdminBypass, createdAt, customBranchPolicies, htmlUrl, id, name, nodeId,
  protectedBranches, protectionRules, updatedAt, url

EXAMPLES
  # List environments for the current repository
  $ gh env list

LEARN MORE
  Use `gh <command> <subcommand> --help` for more information about a command.
  Read the manual at https://cli.github.com/manual
  Learn about exit codes using `gh help exit-codes`

# no environments (TTY)
$ bin/gh env list --repo iamazeem/cli
No environments found in iamazeem/cli

# no environments (no TTY)
$ bin/gh env list | cat

# environments (TTY)
$ bin/gh env list --repo iamazeem/test

Showing 2 of 2 environments in iamazeem/test

NAME          PROTECTION RULES  SECRETS  VARIABLES
Dev           0                 2        3
github-pages  1                 0        0


# environments (no TTY)
$ bin/gh env list --repo iamazeem/test | cat
Dev
github-pages

# environments JSON (TTY)
$ bin/gh env list --repo iamazeem/test --json id,name
[
  {
    "id": 860059220,
    "name": "Dev"
  },
  {
    "id": 4594393556,
    "name": "github-pages"
  }
]


# environments JSON (no TTY)
$ bin/gh env list --repo iamazeem/test --json id,name | cat
[{"id":860059220,"name":"Dev"},{"id":4594393556,"name":"github-pages"}]

# TTY
$ bin/gh env list --repo cli/cli
X Failed to get environments: could not get secrets total count for cli-discuss-automation environment: HTTP 403: Must have admin rights to Repository. (https://api.github.com/repos/cli/cli/environments/cli-discuss-automation/secrets?per_page=1)


# non-TTY
$ bin/gh env list --repo cli/cli | cat
cli-discuss-automation
github-pages
production
staging