doc: replace type names that no longer exist

[Zir0-93]

Four pages name types that are not in the code on main:

• modules/metrics.adoc: MetricsDecorator was renamed to MetricsFilter in a371e6d (decorator: rename Route.Decorator to Route.Filter #2657). The sample under it reads use(new MetricsModule()), but MetricsModule is an Extension and use takes a Route.Filter, so the sentence and both samples now use MetricsFilter.
• mvc-api.adoc: MvcExtension was removed in 0e01cf4 (remove: MvcFactory #3705). Jooby.mvc takes io.jooby.Extension.
• responses.adoc: Context.send(io.jooby.buffer.DataBuffer) was removed in b40f3ef. The overload is send(io.jooby.output.Output).
• value-api.adoc: the Value Factory sample implements io.jooby.value.ValueConverter. There is no such interface. ValueFactory.put takes io.jooby.value.Converter, which has the convert(Type, Value, ConversionHint) method the sample overrides.

Not touched: migration/4.x.adoc line 76 gives io.jooby.value.ValueConverter as the 4.x name, and modules/graphql.adoc still has the "GraphQL Playground" section for the module removed in d97a058 (#3710).

I have not built the docs.

Found with Striff, a tool I work on that checks documentation against code. The full report for this repository has the details.