omni-node: add metadata checks for runtime/parachain compatibility

[iulianbarbu]

Description

Get runtime's metadata, parse it and verify pallets list for a pallet named ParachainSystem (for now). Ideally we'll add others 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

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