weep credential_process --generate should append aws config file

[jzhuge]

Describe the bug
weep credential_process --generate overwrites the aws config file. It is not desirable.

To Reproduce
Steps to reproduce the behavior:

1. Install weep and run weep credential_process --generate

Expected behavior
The generated profiles should be appended to the aws config file.

Desktop (please complete the following information):

• OS: MacOS Ventura 13.04