[FIX] Multi Select isn't working in Export Messages

[PriyaBihani]

• I have read the Contributing Guide - https://github.com/RocketChat/Rocket.Chat/blob/develop/.github/CONTRIBUTING.md#contributing-to-rocketchat doc
• I have signed the CLA - https://cla-assistant.io/RocketChat/Rocket.Chat
• 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 necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Proposed changes (including videos or screenshots)

While exporting messages, we were not able to select multiple Users like this:

WhatsApp.Video.2021-03-22.at.12.25.34.mp4

Now we can select multiple users:

WhatsApp.Video.2021-03-22.at.12.21.55.mp4

Issue(s)

#21235

Steps to test or reproduce

Further comments

We don't need to make changes in the server because it was already equipped with handling multiple users.