Sidebar "join" button text change

[amilliiee]

Contributor checklist

• [x] This pull request is on a separate branch and not the main branch

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Description

This PR updates the "Join" button on the home page to "Join activist" and fixes the button resizing issue that appears with the change.

The updates were:

• added new key in en-US.json
• updated DropdownUserOptions to use new key
• included whitespace-nowrap in DropdownBase MenuButton

Related issue

• 842

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[github-actions[bot]]

Thank you for the pull request!

The activist team will do our best to address your contribution as soon as we can. The following is a checklist for maintainers to make sure this process goes as well as possible. Feel free to address the points below yourself in further commits if you realize that actions are needed :)

If you're not already a member of our public Matrix community, please consider joining! We'd suggest using Element as your Matrix client, and definitely join the General and Development rooms once you're in. It'd be great to have you!

Maintainer checklist

• [x] The commit messages for the remote branch should be checked to make sure the contributor's email is set up correctly so that they receive credit for their contribution

  • The contributor's name and icon in remote commits should be the same as what appears in the PR
  • If there's a mismatch, the contributor needs to make sure that the email they use for GitHub matches what they have for git config user.email in their local activist repo

• [x] The TypeScript and formatting workflows within the PR checks do not indicate new errors in the files changed

• [x] The CHANGELOG has been updated with a description of the changes for the upcoming release and the corresponding issue (if necessary)