Update browser.rb to accept mobile device name

What does this MR do?

Updates browser.rb to accept mobile device names when integrating with Sauce Labs. Part of gitlab-com/www-gitlab-com#11567 (closed) for mobile browser test coverage. Consequently enables desktop Safari and Firefox browser integrations as well.

Can use any of the device names listed in the latest version of iOS or Android(14.3 and 11 respectively) when paired with its default browser(safari or chrome). Eg:

• iPhone: QA_BROWSER='safari' QA_REMOTE_MOBILE_DEVICE_NAME='iPhone 12 Simulator'
• iPad: QA_BROWSER='safari' QA_REMOTE_MOBILE_DEVICE_NAME='iPad Simulator'
• Android: QA_BROWSER='chrome' QA_REMOTE_MOBILE_DEVICE_NAME='Android GoogleAPI Emulator'

Note: Tests do not yet pass on phones as navigation expectations still need to be updated as noted in gitlab-com/www-gitlab-com#11567 (closed) . This change is just for communicating browser and device preferences in Sauce Labs. The next steps are creating a proxy to protect credentials, updating navigation page objects, and then adding a :mobile test tag.

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