Unnecessary trailing .conf in default nginx stream configuration file

[PeterWang-dev]

Describe the bug
There's an trailing .conf in default nginx stream configuration file.
That unnecessary suffix leads to the bug that nginx doesn't read conf generated from UI.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Manage Streams'

2. Click on 'Add.'

3. Create an configuration and enable it.

   server {
      listen 443;
   }
   

4. Attach to docker container and check the opened ports.

5. Observe that the port isn't listened as the config file UI generated file has no .conf suffix and do not read by nginx.

6. Change the name and add .conf suffix. Everything in stream works out of box.

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
If applicable, add screenshots to help explain your problem.

Info (please complete the following information):

• Server: Docker
• Nginx UI Version: 2.0.0-beta.26
• Your Browser: Firefox

Additional context
.conf suffix should be deleted in nginx conf, similar as site-enabled/*