fix: miner: init miner's with 32GiB sectors by default

[arajasek]

Related Issues

Fixes #9359

Proposed Changes

We had per-network defaults before, but that got removed in #9267. That's fine, but let's default to a mainnet-friendly size.

We could also have a DefaultMinerInit build var that we set differently across the networks, but I'd rather not.

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs,perf, refactor, revert, style, test
  • area: api, chain, state, vm, data transfer, market, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet, deps
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in https://lotus.filecoin.io or Discussion Tutorials.
• CI is green

[Reiers]

lotus-miner init --owner=t1kfdps3ts7qu5x7ebek3ddob4xtuuri4py54bw5i --worker=t3u4sl3d4prw24ipkbpo7g4ilod2n27yoreb73ay6yixhypsr3chtzt4ryeik3adj65y6ppxl6qcvytdqj7yta --no-local-storage

2022-09-23T17:06:56.844+0200	ERROR	main	lotus-miner/init.go:269	Failed to initialize lotus-miner: creating miner failed:
    main.storageMinerInit
        /home/reiers/lotus/cmd/lotus-miner/init.go:552
  - failed to parse sector size: invalid size: ''
2022-09-23T17:06:56.844+0200	INFO	main	lotus-miner/init.go:274	Cleaning up /home/reiers/fullnode/LOTUS_MINER after attempt...
ERROR: Storage-miner init failed