misc: Add test ids for prejoin buttons

react/features/base/premeeting/components/web/ActionButton.js

             {children}
             {hasOptions && <div
                 className = 'options'
+                data-testid = 'prejoin.joinOptions'
                 onClick = { disabled ? undefined : onOptionsClick }>
                 <Icon
                     className = 'icon'

react/features/prejoin/components/Prejoin.js

                                     content = { <div className = 'prejoin-preview-dropdown-btns'>
                                         <div
                                             className = 'prejoin-preview-dropdown-btn'
+                                            data-testid = 'prejoin.joinWithoutAudio'
                                             onClick = { joinConferenceWithoutAudio }>
                                             <Icon
                                                 className = 'prejoin-preview-dropdown-icon'
                                             onClick = { _showDialog }>
                                             <Icon
                                                 className = 'prejoin-preview-dropdown-icon'
+                                                data-testid = 'prejoin.joinByPhone'
                                                 size = { 24 }
                                                 src = { IconPhone } />
                                             { t('prejoin.joinAudioByPhone') }