This removes the `appsmithctl migrate` command which can migrate an
Appsmith instance from on EC2 instance to another, using SSH. Why are we
removing it?
1. It's not documented on docs.appsmith.com at all.
2. The problem is better solved with a combination of `appsmithctl
backup` and `appsmithctl restore`, with much _more_ flexibility.
This broke when we changed the way RTS stores version information. This
was never the right way to get the version in the `backup` command and
this PR fixes it, by getting the version from `info.json`.
Failure error:
```
Error: ENOENT: no such file or directory, open '/opt/appsmith/rts/version.js'
```
Move the files that are copied into the Docker image, into an `fs`
folder, that reflects the folder structure of that in the image. This
means two things right away:
1. A single `COPY` instruction in `Dockerfile` is enough to copy all the
files to their places.
2. The structure of files in the repo reflects that in the Docker image.
This makes working with the files/folders and troubleshooting with them
much easier.
❗ Note: **There's actually only 3 files changed, rest are just moved.**
