update funder's league page

### Description

In preparation to have a new matching pools filter the internal team will be removing the categories filter and replacing it with a matching pools filter.

As a user who is looking to become part of the funder’s league, I want a clear form to convey my funding preferences for grants.

The scope of this ticket will include some changes and updates to the funder’s league form.

### Changes

- Replaced top part with gradient
- Replaced “Where do you want to allocate funds to” to a simple dropdown
- Removed “Categories” and replaced it with “Matching Rounds
- All other functionality and links stay the same

### Design

https://www.figma.com/file/8m2fteCPmm3yHXdoBTAwYv/Exploration---GR12-Grant-Creation?node-id=0%3A1

### Acceptance Criteria

GIVEN I am a user looking to be part of the funder's league and contribute my pledge for future matching pools
WHEN I see the funder's league form
THEN I see the default form state.

GIVEN I am a user on the funder's league form
WHEN I have selected "to one or more grant matching rounds" for where I want to allocate funds to
THEN the form offers the ability to input which matching rounds I would like to allocate funds to.

GIVEN I am a user on the funder's league form and have selected "to one or more grant matching rounds" for where I want to allocate funds to
WHEN the form changes to offer the ability to input which matching rounds I would like to allocate funds to
THEN the input field will have the same functionality as on the grants creation form.

GIVEN I am a user on the funder's league form
WHEN I have selected "to one or more grant collections" for where I want to allocate funds to
THEN the form offers the ability to input which collections I would like to allocate funds to.