fix(docker): ensure that the app runs with webapp

[dcshzj]

Problem

The ECS tasks are running the web application as root, which causes permission issues on EFS when co-existing with the EB instances.

Solution

Breaking Changes

• [ ] Yes - this PR contains breaking changes
• [x] No - this PR is backwards compatible with ALL of the following feature flags in this doc

Bug Fixes:

• Ensure that we execute the docker container as the webapp user.

Tests

• [ ] Create a new folder in the images page for any repo.
• [ ] Perform a task exec and open a shell session with an ECS container.
• [ ] Change directory to the repo chosen earlier and go into the images folder.
• [ ] Perform ls -l and verify that the newly created folder is owned by webapp:webapp.
• [ ] Perform ls -ln and verify that the newly created folder is owned by 900:900.

Deploy Notes

• [ ] After deployment, bring the traffic routing of prod to 10% ECS and 90% EB.
• [ ] Verify the above tests again on prod while on OGP VPN.
• [ ] Attempt to edit a page and ensure that you are able to save successfully.
• [ ] Disconnect from OGP VPN and ensure that you refresh your browser tab to avoid sticky sessions.
• [ ] Attempt to upload an image into the newly created folder and verify that you can successfully upload.
• [ ] Attempt to edit a page and ensure that you are able to save successfully.