Respect assets mode config in controller

[HypeMC]

Q	A
Bug fix?	yes
New feature?	no
Deprecations?	no
Issues	-

Currently the SwaggerUiController doesn't respect the assets_mode configuration added in #2251.

nelmio_api_doc:
  html_config:
    assets_mode: cdn

As far as I can tell, there's no reason for the default any more as it can be set through the configuration and overridden in the DumpCommand command using the html-config option.

[DjordyKoert]

Thank you @HypeMC :)

[DominicLuidold]

First of all: @HypeMC thanks!

Just as a quick side note: this has (unintentionally?) changed the default asset mode to CDN which was a bit unexpected as the release notes didn't mention that change (we noticed as our API docs weren't working in review environments anymore after the update, because the CDN calls got blocked by CSP).

/cc @DjordyKoert