mc dev-proxy does not read --passkey from MDSP_PASSKEY variable like other commands

**Describe the bug**
See title

**To Reproduce**
```
PS> $env:MDSP_PROXY="superSecretPasskey"
PS> mc dev-proxy --mode credentials

you have to specify passkey for credentials mode
PS>
```  

**Expected behavior**
Should work like --passkey
```
PS> mc dev-proxy --mode credentials --passkey "superSecretPasskey"

Mode credentials

CORS support on
...
```