[Feature]: update join conference by URL screen to make input more obvious

[dustinsgoodman]

Is your feature request related to a problem? Please describe.

When joining a conference by URL, the input field is not immediately recognizable as an input field and it has limited with for longer conference names.

Describe the solution you'd like

Let's slightly redesign this screen by doing the following:

• Change the page title to be "Join Conference by Slug" instead of "Enter Conference URL"
• Update the previous screen to say "Enter conference slug"
  
• Create an input with label (similar to login screens)
  • label: Conference Slug
  • Placeholder: conference-url
• Move the "continue" button up on the screen to be near the form

Additional context

No response