Manage context environment variables

## Usage

`circleci context secret <command> [flags]`

## Available Commands

| Command  | Description                                   |
| -------- | --------------------------------------------- |
| `delete` | Delete an environment variable from a context |
| `list`   | List environment variables in a context       |
| `set`    | Set an environment variable in a context      |

## Flags

Global flags: `-c, --config`, `--debug`, `--no-color`, `-q, --quiet` — see `circleci --help`.

## Details

List, set, and delete environment variables stored in a CircleCI context.

Context environment variables are injected into jobs that reference the
context. Variable values are never returned by the API after being set.

