feat: load images from sub-folders

[saw-jan]

Description

Implement loading ocis images from the sub-directories.

Related Issue

• Resolves [feature] embed images #27

Motivation and Context

How Has This Been Tested?

• test environment: ✋ and 🤖

Screenshots (if appropriate):

## Slide With oCIS Image - sub

![webdriver_ill.jpg](./sub/inner/webdriver_ill.jpg)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Tests only (no source changes)
• Documentation only (no source changes)
• Maintenance (e.g. dependency updates or tooling)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation updated

[S-Panta]

Works in my setup but it take some millisecond to render the image if there are more subfolder.

[S-Panta]

Tested Manually. LGTM