Override scripts for custom `ckan` images fail: `sudo` not installed

## Overview

The [`ckan/setup/start_ckan.sh.override`](https://github.com/ckan/ckan-docker/blob/master/ckan/setup/start_ckan.sh.override) file uses `sudo` to impersonate the `ckan` user. However, `sudo` is not available in the Alpine-based container images. As a result, if you follow the instructions in [step 5 of the top-level `README.md`](https://github.com/ckan/ckan-docker/blob/master/README.md?plain=1#L127) and install the override script to create a custom `ckan` image, the script fails when a container is started with that custom image (see the "Demonstration" section).

I did not try to build the development image, but looking at [the corresponding override file](https://github.com/ckan/ckan-docker/blob/master/ckan/setup/start_ckan_development.sh.override), this error also affects that one.

As a note, it appears that the `start_ckan.sh.override` script is a copy of [`ckan-2.10/base/setup/start_ckan.sh` in the `ckan/ckan-docker-base` repo](https://github.com/ckan/ckan-docker-base/blob/main/ckan-2.10/base/setup/start_ckan.sh). (Note, however, that the `ckan/ckan-docker-base` version of this script does **not** use `sudo`, so presumably this override file got out of sync with upstream.) Similarly, the `start_ckan_development.sh.override` file seems to be a copy of [`ckan-2.10/dev/setup/start_ckan_development.sh` in the `ckan/ckan-docker-base` repo](https://github.com/ckan/ckan-docker-base/blob/main/ckan-2.10/dev/setup/start_ckan_development.sh).

It would probably be worth adding comments to the override files or to the `README` stating this, so that people who encounter issues with these in the future can understand how they relates to the base images.

### Demonstration

I cloned the current `master` (commit 6bbc482e0) and made this change to `ckan/Dockerfile`:

```diff
$ git diff
diff --git a/ckan/Dockerfile b/ckan/Dockerfile
index 75001e9..236f3b0 100644
--- a/ckan/Dockerfile
+++ b/ckan/Dockerfile
@@ -10,3 +10,5 @@ RUN echo ${TZ} > /etc/timezone
RUN if ! [ /usr/share/zoneinfo/${TZ} -ef /etc/localtime ]; then \
cp /usr/share/zoneinfo/${TZ} /etc/localtime ;\
fi ;
+
+COPY setup/start_ckan.sh.override ${APP_DIR}/start_ckan.sh
```

Then, I ran `docker compose build` and `docker compose up`. The `ckan` container eventually died. Here are its logs, minus some extremely lengthy traceback that I believe occurs because the invocation of `sudo python3 prerun.py` fails due to `sudo`:

```text
$ docker logs ckan
beaker.session.secret =
Setting beaker.session.secret in ini file
/srv/app/start_ckan.sh: line 19: sudo: not found
Set up ckan.datapusher.api_token in the CKAN config file
2023-09-05 17:36:00,458 INFO [ckan.cli] Using configuration file /srv/app/ckan.ini
2023-09-05 17:36:00,459 INFO [ckan.config.environment] Loading static files from public
2023-09-05 17:36:00,680 INFO [ckan.config.environment] Loading templates from /srv/app/src/ckan/ckan/templates
2023-09-05 17:36:01,115 WARNI [ckanext.reclineview.plugin] The Recline-based views are deprecated andwill be removed in future versions
2023-09-05 17:36:01,137 INFO [ckan.config.environment] Loading templates from /srv/app/src/ckan/ckan/templates
2023-09-05 17:36:02,293 WARNI [ckan.config.middleware.flask_app] Extensions are excluded from CSRF protection! We allow extensions to run without CSRF protection but it will be forced future releases. Read the documentation for more information on how to add CSRF protection to your extension.
Traceback (most recent call last):
File "/usr/lib/python3.10/site-packages/sqlalchemy/engine/base.py", line 1900, in _execute_context
self.dialect.do_execute(
File "/usr/lib/python3.10/site-packages/sqlalchemy/engine/default.py", line 736, in do_execute
cursor.execute(statement, parameters)
psycopg2.errors.UndefinedTable: relation "user" does not exist
LINE 2: FROM "user"
^
(... omitting lengthy traceback related to this ...)

/srv/app/start_ckan.sh: Ignoring /docker-entrypoint.d/* (not an sh or py file)

/srv/app/start_ckan.sh: line 54: sudo: not found
```

## Suggested Fixes

For the `start_ckan.sh.override` file, remove the instances of `sudo -u ckan -EH` from the file. It's worth pointing out that this results in the application running as root, which might not be ideal.

It's also worth noting that because the script does not run with the `-e` flag, the first `sudo` call in the current script does not cause the container to die immediately. I verified that changing the shebang line to `#!/bin/sh -e` causes the script to fail as soon as that first `sudo` is hit, but I don't know if that's really desirable; are some failures OK or expected? (This is really an upstream `ckan/ckan-docker-base` question; if there is interest, I can log an issue there as well, if needed.)

For `start_ckan_development.sh.override`, the approach is less clear, since I haven't actually tested it. Removing `sudo -u ckan -EH` probably needs to happen. However, the `ckan/ckan-docker-base` version of the script has [an extra `su` command on the last line](https://github.com/ckan/ckan-docker-base/blob/main/ckan-2.10/dev/setup/start_ckan_development.sh#L99) that appears to be used to run CKAN as the `ckan` user.

Maybe using `su ckan -c ...` is the best path forward for both override scripts? I don't know enough about how CKAN runs / expects to run to say for sure, but it is worth noting that this difference exists.