okta-awscli duplicates the config file when appending to it

[tdmalone]

Describe the bug
When ~/.okta-aws already exists and okta-awscli --config is run, it results in the entire existing contents of the config file being appended. It likely needs to either append only the new profile, OR instead of appending, replace the old contents with the new contents, rather than attempting to do both.

To Reproduce
Steps to reproduce the behavior:

1. With an existing profile already in place, run okta-awscli --config
2. Enter y when prompted, to proceed to append the new profile
3. Answer the questions as necessary
4. The command succeeds, but when trying to use okta-awscli, an error will be received due to duplicate profiles

Expected behavior
The new profile to append, rather than the existing contents of the file also being appended.

Output

Environment (please complete the following information):

• OS: macOS
• Version of okta-awscli: 0.5.4

Additional context

[jwflynn]

I see the same behavior in windows