Add extension placeholder for serialized medias

[Prokyonn]

No description provided.

[Prokyonn]

@alexander-schranz @wachterjohannes to prevent the BC break, we could maybe add a config like this:

sulu_headless:
    media:
        use_preferred_extension: true

WDYT?

[alexander-schranz]

Suggested change

	$mediaData['preferredExtension'] = $preferredExtension;
	$mediaData['formatPreferredExtension'] = $preferredExtension;

So they are beside each other in the json response.

[alexander-schranz]

I think formatUri, formatPreferredExtension should be null if there is no preferredExtension as I think that indicates that there are no formats available for this media. E.g. .doc, .xls, ...

[alexander-schranz]

would replace @string@ in formatUri to check the Uri is as expected.

[alexander-schranz]

Can we create a real instance of LocalFormatCache so we avoid this mock.

[alexander-schranz]

@Prokyonn if somebody is using ^0.9 they will not get automatically 0.10, as ^ in pre stable versions is handled like 0.9.* so active update is required and so I'm fine with this bc break and no additional flag.

[alexander-schranz]

Suggested change

	"formatUri": "/media/1/{format}/media-1.{extension}?v=1-0",
	"preferredExtension": "png"
	"formatUri": "/media/1/{format}/media-1.{extension}?v=1-0",
	"formatPreferredExtension": "png"

[wachterjohannes]

@alexander-schranz @wachterjohannes to prevent the BC break, we could maybe add a config like this:

sulu_headless:
    media:
        use_preferred_extension: true

WDYT?

@Prokyonn would also go with a flag and throw a deprecation message when it is not set! else the PR LGTM.

[Prokyonn]

as discussed internally, we'll omit the configuration BC layer, because of

if somebody is using ^0.9 they will not get automatically 0.10, as ^ in pre stable versions is handled like 0.9.* so active update is required and so I'm fine with this bc break and no additional flag.