feat: allow skipping payments adjustments in the gh action

### Description

The upload action computes a funding plan and, when more funds are needed, performs the top-up automatically (`upload-action/src/filecoin.js:131-158`). There is no way to tell the action to leave payment state alone.

Some users manage allowances and funding outside the action: their own deposit/allowance flow, a shared treasury, or a separate setup step. For them the action mutating payment state is unwanted and can fight their own management.

### Proposed approach

Add an action input (e.g. `skipPaymentSetup: true`) that bypasses the funding-plan top-up and uploads with whatever allowances and balance already exist. When set:

- skip the `calculateFilecoinPayFundingPlan` / `executeTopUp` adjustment.
- still surface current account status so the run stays debuggable.
- fail clearly if existing funds/allowances are insufficient, rather than silently topping up.

### Done criteria

- New input skips the action's payment adjustment when enabled; default keeps current behavior.
- Upload proceeds on existing allowances/balance with no deposit or allowance changes.
- Insufficient-funds case fails with an actionable message pointing at external setup.
- Documented in `upload-action/action.yml` and the action README.