Hi,

In `debhelper/13.26`, `dh_assistant list-guessed-dh-config-files` will
now report `debhelper` commands that does not declare which config files
it supports. As an example:

```shell
$ dh_assistant list-guessed-dh-config-files
{
    "commands-not-introspectable": [
       "dh_autoreconf",
       "dh_strip_nondeterminism"
    ],
    # ... more JSON here, omitted for brevity
}
```
(The output only lists commands active for the source package, so the
commands from this package will be absent if they are not in the default
sequence)

This is in turn used by `debputy migrate-from-dh` to warn people when
`debhelper` config files might be overlooked.

I believe this bug can be fixed by filling out the following template
and adding it in the `dh_elpa` command (the file found PATH - imports
are not followed):

```
# INTROSPECTABLE: CONFIG-FILES pkgfile(elpa) pkgfile(emacsen-X)
```

Add one `pkgfile(emacsen-X)` for each different value of `$piece` in
`maybe_install_helper`. There might be other cases (I only did a very
trivial eyeball scan of the code).

For `dh_elpa_test`, I think it should be:

```
# INTROSPECTABLE: CONFIG-FILES path(debian/elpa-test)
```

Note, if the commands can be skipped when these are not present, then a
`NOOP` promise might be the better option. I did not check for this in
either case (but I suspect the cannot).

Please review `doc/PROGRAMMING.md` in debhelper/13.26 for alternatives
or reply back to me for assistance.

Best regards,
Niels