docs/Run your node: Update hardware requirements

Update the current hardware requirements, specifically storage.

Currently, they portray impression that running a Consensus + Sapphire node (Validator + Compute node) requires 2TB of the disk space. This are hardware requirements for nodes that are able to serve all historical state... Serving historical state is NOT validators responsibility.

Instead they should have pruning set to few weeks max - see https://github.com/oasisprotocol/docs/pull/1526. This makes them fast, enables checkpoint creation that is quick and has little IO overhead, resulting in a much smaller disk footprint, and thus cost. E.g. 100GB should be enough.

Finally, we should organize Run your node sections from most to least accessible options. E.g. hardware requirements should reflect this order:

1. Stateless
2. Non-Validator/Paratime-Client (with pruning)
3. Validator/Executor (with pruning)
4. Observer (with pruning)
5. Non-Validator/Paratime-Client/Observer with all historical state.
6. Keymanager/Sentry/Archive

Partially overlaps with #1469.