Propose and approve a spend of treasury funds.

## Dispatch Origin

Must be [`Config::SpendOrigin`] with the `Success` value being at least
`amount` of `asset_kind` in the native asset. The amount of `asset_kind` is converted
for assertion using the [`Config::BalanceConverter`].

## Details

Create an approved spend for transferring a specific `amount` of `asset_kind` to a
designated beneficiary. The spend must be claimed using the `payout` dispatchable within
the [`Config::PayoutPeriod`].

### Parameters
- `asset_kind`: An indicator of the specific asset class to be spent.
- `amount`: The amount to be transferred from the treasury to the `beneficiary`.
- `beneficiary`: The beneficiary of the spend.
- `valid_from`: The block number from which the spend can be claimed. It can refer to
  the past if the resulting spend has not yet expired according to the
  [`Config::PayoutPeriod`]. If `None`, the spend can be claimed immediately after
  approval.

## Events

Emits [`Event::AssetSpendApproved`] if successful.

- **Problem Statement:** PolkaWorld is requesting 266,652 USDT to support its operations for the upcoming year (April 2025 – March 2026) to continue delivering high-quality content and engagement in the Polkadot ecosystem.
- **Significance:** PolkaWorld's proposal aims to enhance regional engagement, bridge communication gaps, and foster growth within the Polkadot community, especially in Chinese-speaking regions.
- **Proposed Solution:** Delivering 288 articles, 72 livestreams, 48 educational videos, 12 in-depth interviews, and managing bilingual Twitter accounts to maintain community education and engagement.
- **Expected Outcomes:** Increased visibility, improved content quality, strengthened ecosystem development, and enhanced user metrics through consistent content creation, live broadcasts, educational videos, interviews, and social media management.

#1522 PolkaWorld Ops and Maintenance proposal：2025.4 - 2026.3