Support mermaid js

[PrajwolAmatya]

Description

This PR adds support for mermaid js in the presentation slide to illustrate different diagrams.

Screenshot

markdown content:

    ## Mermaid JS

    ```mermaid
    sequenceDiagram
        participant Alice
        participant Bob
        Alice->>John: Hello John, how are you?
        loop HealthCheck
            John->>John: Fight against hypochondria
        end
        Note right of John: Rational thoughts <br/>prevail!
        John-->>Alice: Great!
        John->>Bob: How about you?
        Bob-->>John: Jolly good!
    ```

rendered Slide:

Relate WP

https://community.openproject.org/projects/revealjs/work_packages/60581/activity