Handle automatic backup files

```
$ npm run upgrade

> @carto-chasse/appwrite-local@0.4.1 upgrade
> ./scripts/upgrade.sh

[INFO] Upgrading Appwrite stack to version 1.8.0...
Unable to find image 'appwrite/appwrite:1.8.0' locally
1.8.0: Pulling from appwrite/appwrite
3ba9b623cca8: Pull complete
a46b170eccf1: Pull complete
dad9acb3da5c: Pull complete
4f4fb700ef54: Pull complete
903dc772fc3b: Pull complete
acd2cb183db2: Pull complete
6f14603aace2: Pull complete
dc31d7f50a12: Pull complete
a0885627b4fb: Pull complete
15bd1c999535: Pull complete
c55f846d8054: Pull complete
ba7bfb514835: Pull complete
b30776113751: Pull complete
45ffbc23ae18: Pull complete
Digest: sha256:598962a5fd8d6c689edf68cdf45494e4e4375d541e85fddee8c56ade242b6965
Status: Downloaded newer image for appwrite/appwrite:1.8.0
Skipped SMS processing. Missing "_APP_SMS_PROVIDER" or "_APP_SMS_FROM" environment variables.
Skipped SMS processing. Missing "_APP_SMS_PROVIDER" or "_APP_SMS_FROM" environment variables.
Starting Appwrite installation...
Previous installation found, do you want to overwrite it (a backup will be created before overwriting)? (Y/n)
y
Compose file found, creating backup: docker-compose.yml.1761087054.backup
Env file found, creating backup: .env.1761087054.backup
[...]
```

If responding Y, it generates backup files. But we may already have those if `npm run backup` was run.

So, if they do exist and the user responds Y, the new backup files could/should be ignored.