Delete user does not work for IAM based users

[422158]

Describe the bug
Delete user method does not work due to missing url escaping.
Following code does not work because the delete method does not escapes the username, when sending delete request to Atlas mongo api.

groupID := xxxxxxxxxxxx
username := "arn:aws:iam::977946299200:role/complicated-stack-heyhou-eu-we-9e2e2c92c26e1fd5d571582267c271fe"
dbName := $external

resp, err := client.DatabaseUsers.Delete(context.Background(), dbName, groupID, username)

If i escape all the dangerous characters in the url, delete method completes succesfully.

groupID := xxxxxxxxxxxx
username := url.QueryEscape("arn:aws:iam::977946299200:role/complicated-stack-heyhou-eu-we-9e2e2c92c26e1fd5d571582267c271fe")
dbName := $external

resp, err := client.DatabaseUsers.Delete(context.Background(), dbName, groupID, username)

Expected behavior
Username should be escaped automatically.

Logs
If applicable, add logs to help explain your problem.

Desktop (please complete the following information):

• OS: linux
• Lib Version: 0.7.2

Additional context
Add any other context about the problem here.

[gssbzn]

Resolved via #199