/telegraf/plugins GET - query parameter type with unknown value returns HTTP 500

__Steps to reproduce:__
List the minimal actions needed to reproduce the behavior.

1. create a request to `/telegraf/plugins` with the query param `type` assigned a value that matches no known type
2. send the request

example

https: //twodotoh-dev-bonitoo-kk.remocal.influxdev.co/api/v2/telegraf/plugins?type=koala

__Expected behavior:__
I expected that either
* the response would be HTTP 200 with an empty set of plugins
* or, the response would be HTTP 400 with an error message that the type is invalid or not found along perhaps with an enum of available types

In general, I would expect certain common exception use cases, like a parameter with a non-matching or invalid value, to be handled gracefully.

__Actual behavior:__
The server throws HTTP 500.

__Environment info:__

Testing against K8S-IDPE remocal.

```
commit 78d0c45205ea0bc0fb9c365ff2eb4f5f2595270a (HEAD -> master, origin/master, origin/HEAD)
Author: influx-acs[bot] <107396960+influx-acs[bot]@users.noreply.github.com>
Date: Thu Nov 10 08:31:58 2022 +0000
```
__Caution - Cloud Pipeline__

I see there is a grace test `test/cloud/telegrafs.test.js:276` that asserts the HTTP 500 response. If this issue should be fixed, so that this case is handled as described above, this test will also need to be updated.

Start with the GET /telegraf/plugins behavior described in the reproduction and the existing assertion at test/cloud/telegrafs.test.js:276. Determine the intended response for an unknown type, then update the implementation and test so the request no longer produces an HTTP 500 and the test reflects the agreed behavior.

Written by the indexing model from the issue text.