Added changes to fix the markdown for mention user

[brf153]

Proposed changes

Fixed the bug in the markup so that it now works for user mentions.

Issue(s)

closes #5302
Depends on RocketChat/fuselage#1228

How to test or reproduce

Create a message using various Markdown formatting options and include mentions using '@'. For instance, *Hello @brf153, how are you?*

Screenshots

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To

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Documentation update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added the necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Additional Comment

I need to add changes to the fuselage repository of Rocket Chat. After that, this pull request will work fine.

[diegolmello]

Thanks for your contribution, @brf153!
We're going to evaluate this asap.
Just be aware we're in the middle of a long release, so it might take longer than expected to review it.

[brf153]

@diegolmello Sure sir