omni-node: add metadata checks for runtime/parachain compatibility (#6450)

# Description

Get runtime's metadata, parse it and verify pallets list for a pallet
named `ParachainSystem` (for now), and block number to be the same for
both node and runtime. Ideally we'll add other pallets checks too, at
least a small set of pallets we think right away as mandatory for
parachain compatibility.
Closes: #5565 

## Integration

Runtime devs must be made aware that to be fully compatible with Omni
Node, certain naming conventions should be respected when defining
pallets (e.g we verify parachain-system pallet existence by searching
for a pallet with `name` `ParachainSystem` in runtime's metadata). Not
finding such a pallet will not influence the functionality yet, but by
doing these checks we could provide useful feedback for runtimes that
are clearly not implementing what's required for full parachain
compatibility with Omni Node.

## Review Notes

- [x] parachain system check
- [x] check frame_system's metadata to ensure the block number in there
is the same as the one in the node side
- [x] add tests for the previous checking logic
- [x] update omni node polkadot-sdk docs to make these conventions
visible.
- [ ] add more pallets checks?

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Signed-off-by: Iulian Barbu <[email protected]>
Co-authored-by: Alexandru Vasile <[email protected]>
Co-authored-by: Michal Kucharczyk <[email protected]>