feat: Implement hextra hero-section

[fmunteanu]

New Feature Proposal: Hero Section

On Hextra front-page, I need the ability to insert a h2 heading, defining additional section titles. For example, adding a subtitle above hextra/feature-grid.

Proposed Solution

I created the following layouts/shortcodes/hextra/hero-section.html shortcode, implementing a section.

Live Example

Visit https://axivo.com/k3s-cluster/.

Shortcode Usage

Example of hextra/hero-section shortcode usage, default header size is h2:

{{< hextra/hero-section >}}
  Used Technologies
{{< /hextra/hero-section >}}

Example of hextra/hero-section shortcode usage, with h3 header size:

{{< hextra/hero-section header="h3" >}}
  Used Technologies
{{< /hextra/hero-section >}}

Example of hextra/hero-section shortcode usage, with h4 or greater header size:

{{< hextra/hero-section header="h4" >}}
  Used Technologies
{{< /hextra/hero-section >}}

Frontage View

The Used Technologies section title, using default h2 header:

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[fmunteanu]

Related to #388 and #389.