[Feature Request]. Add diagrams(mermaid) attachment support

**Is your feature request related to a problem? Please describe.**
The problem with big comprehensive test cases is that they have a lot of dependencies. Sometimes it's better to describe with diagrams, like [mermaid](https://mermaid.js.org/).

**Describe the solution you'd like**
based on [docs](https://allurereport.org/docs/attachments/#visual-comparisons) add a new application type for attachments: E.g. `application/vnd.allure.diagrams.mermaid`.

Or if we transform in code:
```ts
import { test } from '@playwright/test'
import { allure } from 'allure-playwright'

test('some test', async () => {
allure.attachment('some diagram name', `
graph TD
A[Client] -->|tcp_123| B
B(Load Balancer)
B -->|tcp_456| C[Server1]
B -->|tcp_456| D[Server2]
`, 'application/vnd.allure.diagrams.mermaid')
})
```

**Describe alternatives you've considered**
For now, you can create attachments by typing `text/html` with the following content
```html

            graph TD 

            A[Client] --> B[Load Balancer] 

            B --> C[Server1] 

            B --> D[Server2]

    

import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
mermaid.initialize({ startOnLoad: true });

```

**Additional context**
1. Why mermaid? Since it provides a lot of kinds of diagrams - pie charts, mindmap, class diagrams, graphs.
2. `application/vnd.allure.diagrams.*` gives a flexible approach for other kind of diagram providers, like [plantUML](https://plantuml.com/)
3. Supporting mermaid will be a good point to support markdown style - like [github](https://github.blog/developer-skills/github/include-diagrams-markdown-files-mermaid/). More on [integrations page](https://mermaid.js.org/ecosystem/integrations-community.html). For now it's not supported in TestOps(screen below)

Start with the attachment documentation linked in the request and trace how application types are registered. Confirm the implementation can render Mermaid attachments while preserving the proposed application/vnd.allure.diagrams.mermaid type, and add coverage for the example usage.

Written by the indexing model from the issue text.