Add ability to persist/use CLI configurations

[sgnn7]

Current plan but open RFC

FS structure:

$ tree $HOME
├── 700: drwx------  .conjur/
│   ├── 755: drwxr-xr-x  default.yml -> <profile_nameXX>.yml
│   ├── 600: drw-------  <profile_name1>.yml
│   ├── 755: drwxr-xr-x  <profile_name1>.pem -> <hostname1>.pem
│   ├── 600: drw-------  <profile_name2>.yml
│   ├── 755: drwxr-xr-x  <profile_name2>.pem -> <hostname2>.pem
│   ├── 644: drw-r--r--  <hostname1>.pem
│   ├── 644: drw-r--r--  <hostname2>.pem
...

<profile_name>.yml:

<profile_name>:
    account: <account>
    appliance_url: <url>
    login_id: <login_id>

    # Optional fields. Credentials will be plaintext for now but maybe encrypted later.
    api_key: <api_key>
    ca_bundle: <path>          # default: ./<profile_name>.pem
    debug: <bool>              # default: false
    password: <password>
    insecure: <bool>           # default: false
    tofu: <bool>               # default: true

Usage:

# Create config - omitted profile name == "default" (TBD)
$ cli profile create <url> <account> <login_id> \
    [--tofu <bool>]|[--insecure <bool>]|[--ca-bundle <pem_path>] \
    [--password <password]|[--api-key <api_key>]

# Delete config
$ cli profile delete <profile_name>

# Profile switch for all further CLI commands
$ cli profile <profile_name>

# Show current profile name
$ cli profile

# Use $(cli profile) config
$ cli …

# Use "<profile_name>" config without switching
$ cli -C <profile_name> …

CC: @izgeri / @ismarc / @apotterri / @infamousjoeg / @jodyhuntatx / @ryanprior / @garymoon / @jonahx