[FEATURE] Removal of --renderer flag from command asyncapi new template

[Adi-204]

Why do we need this improvement?

As per generator releases nunjucks is deprecated (which means that user can still use it but it is not recommended) but when I tried to create template with
-r = nunjucks React template was created rather than Nunjucks below is the screenshot.

How will this change help?

Removal of --renderer flag from command asyncapi new template and user will only able to create React template only. Changes in command documentation.

Screenshots

No response

How could it be implemented/designed?

Explain above

🚧 Breaking changes

No

👀 Have you checked for similar open issues?

• I checked and didn't find a similar issue

🏢 Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

Are you willing to work on this issue?

Yes I am willing to submit a PR!

[Adi-204]

Waiting for approval from maintainers.

[Shurtu-gal]

Fair enough. Please open a PR.