feat(server): transcode bitrate and thread settings (#2488)

* support for two-pass transcoding

* added max bitrate and thread to transcode api

* admin page setting desc+bitrate and thread options

* Update web/src/lib/components/admin-page/settings/setting-input-field.svelte

Co-authored-by: Michel Heusschen <59014050+michelheusschen@users.noreply.github.com>

* Update web/src/lib/components/admin-page/settings/setting-input-field.svelte

Co-authored-by: Michel Heusschen <59014050+michelheusschen@users.noreply.github.com>

* two-pass slider, `crf` and `threads` as numbers

* updated and added transcode tests

* refactored `getFfmpegOptions`

* default `threads`, `maxBitrate` now 0, more tests

* vp9 constant quality mode

* fixed nullable `crf` and `threads`

* fixed two-pass slider, added apiproperty

* optional `desc` for `SettingSelect`

* disable two-pass if settings are incompatible

* fixed test

* transcode interface

---------

Co-authored-by: Michel Heusschen <59014050+michelheusschen@users.noreply.github.com>

mobile/openapi/doc/SystemConfigFFmpegDto.md

@@ -8,11 +8,14 @@ import 'package:openapi/api.dart';
 ## Properties
 Name | Type | Description | Notes
 ------------ | ------------- | ------------- | -------------
-**crf** | **String** |  | 
+**crf** | **int** |  | 
+**threads** | **int** |  | 
 **preset** | **String** |  | 
 **targetVideoCodec** | **String** |  | 
 **targetAudioCodec** | **String** |  | 
 **targetResolution** | **String** |  | 
+**maxBitrate** | **String** |  | 
+**twoPass** | **bool** |  | 
 **transcode** | **String** |  | 
 
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