PROMO: (BRAND) Actualize FSD spelling in docs

[azinit]

Background

There is official spelling of FSD "Feature-Sliced Design" I've actualize it in general in docs, but there are maybe some remained issues Need to resolve them with official spelling in EN/RU docs

https://github.com/feature-sliced/documentation/pull/479

Incorrect occurrences

• [x] "Feature Sliced Design"
• [x] "Feature Sliced"
• [x] "Feature-Sliced"
• [x] "feature-sliced"
• [x] "Feature sliced", "feature sliced" (as possible translation issues)

[azinit]

@illright Готово)