chore(docs): Update slack invitation link

[Muditbhatia12]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

The slack link which was put in the welcome to the hyperswitch community mail took some users to the "This link is no longer active " page.
The link has been updated.

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

How did you test it?

Screen.Recording.2025-05-26.at.1.18.27.PM.mov

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
.github/ISSUE_TEMPLATE/config.yml	0% smaller
README.md	Unsupported file format
api-reference/api-reference/payments/Introduction--to--payments.mdx	Unsupported file format
api-reference/intelligent-router-api-reference/overview.mdx	Unsupported file format
api-reference/mint.json	0% smaller
config/deployments/integration_test.toml	Unsupported file format
config/deployments/production.toml	Unsupported file format
config/deployments/sandbox.toml	Unsupported file format
config/development.toml	Unsupported file format
config/docker_compose.toml	Unsupported file format
crates/router/src/services/email/assets/welcome_to_community.html	0% smaller
docs/CONTRIBUTING.md	Unsupported file format
loadtest/config/development.toml	Unsupported file format

[ThisIsMani]

Is there any expiration time for this link?

[Muditbhatia12]

Is there any expiration time for this link?

This link doesnt expire but it has a limit of 400 users who can join via this link.