Add @searchFieldPosition argument

[mkszepp]

Summary

Follow-up on #1752 & #1784, gradually introducing @searchFieldPosition (before-options | trigger).

Example

Single-selection	Multi-selection
@searchFieldPosition="before-options" (default) @searchFieldPosition="trigger"(NEW)	@searchFieldPosition="trigger" (default) @searchFieldPosition="before-options"(NEW)

Description

<PowerSelect /> instances will have @searchFieldPosition set to before-options by default with the option to change it to trigger.
<PowerSelectMultiple /> instances will have @searchFieldPosition set to trigger by default with the option to change it to before-options.

Demo of the new option you will find in docs under https://ember-power-select.com/docs/the-search section "Search field position"

Note: There was duplicated the input field for single, to make non braking changes... This we can maybe resolve in next major

[mkszepp]

@alex-ju released in v8.6.0