Command bot GHA v2 - /cmd <cmd> (#5457)

Closes https://github.com/paritytech/product-engineering/issues/93

- Deprecates old command bot bash scripts. New cmd implementation is
re-written on Python
- Deprecates `sync` command, which was never used
- Benchmarks:
- Uses new
[frame-omni-bencher](https://crates.io/crates/frame-omni-bencher)
- Simplifies usage to only providing a runtime and/or pallet name (even
multiple runtimes or pallets)
- Supports sub-modules (like `/cmd bench --runtime dev --pallet
pallet_asset_conversion_ops`)
- Can regenerate all weights with one command (substrate, polkadot,
cumulus) for provided pallet(s) name
- Adds [subweight](https://crates.io/crates/subweight-core) diff as a
result of bench command