osra289: partners#index controller&view

Add partners#index controller and view

OSRA-289 #Code-Review
I recommend collapsing the `let` & `before` into the body of the `it` block, here and in the next context. Even when additional tests are introduced into these contexts in the future, this approach will prevent mystery guests from showing up.
```ruby
context 'when partner records exist' do
  it 'should not indicate that no partners were found' do
    # setup
    assign(:partners, build_stubbed(:partner))

    # exercise
    render

    # verify
    expect(rendered).not_to match /No Partners found/
  end
end
```

- if you haven't yet, it's worth trying `build_stubbed` or doubles
- it's best to keep setup to a minimum - here, one Partner is enough, especially if we need to hit the db