fix: Correct curl snippets for builtin connector example

[hreeder]

The current curl snippets both give the following error:

{"error":"invalid_client","error_description":"Invalid client credentials."}

This is because the input to the basic auth header is incorrect.

In the case of the public client, the plaintext is missing a : (indicating that public-client is the username portion of the basic auth header), and it also should have the trailing newline stripped.

In the case of the private client, we just need to strip the trailing newline.

Once that was corrected, both examples still fail due to an invalid password, as the previously shown config file sets password rather than admin as the password for the sample user.