Fixes https://github.com/getsentry/self-hosted/issues/3526
Previously, if this was executed:
```bash
./scripts/backup.sh --no-report-self-hosted-issues
```
The final backup command that will be executed is:
```bash
docker compose run -v "${PWD}/sentry:/sentry-data/backup" --rm -T -e SENTRY_LOG_LEVEL=CRITICAL web export --no-report-self-hosted-issues /sentry-data/backup/backup.json
```
Which is invalid. This PR strips all known flags specific to self-hosted before passing it onto Sentry.
One other option is to enable "ignore unknown options" on click (the CLI dependency) on Sentry, but I don't want to go to that route.
