OpenAPI 3.1.0 support: add OpenAPI 3.1.0 support in Badge

[char0n]

We currently do not render badge for OpenAPI 2.0.

For OpenAPI 3.0.x and OpenAPI 3.1.0 we render the following badge:

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The goal of this issue is to implement the badge in the following way:

OpenAPI 3.0.x

For OpenAPI 3.0.x definition we'll render 3.0 inside the badge

OpenAPI 3.1.0

For OpenAPI 3.1.0 definition we'll render 3.1 inside the badge

[char0n]

Badge rendering for OpenAPI 3.1.0 definitions:

Badge rendering for OpenAPI 3.0.x definition: