feat: add custom db weights

[weichweich]

fixes KILTProtocol/ticket#2066

Default rocksdb weights are:

read: 25_000 * constants::WEIGHT_PER_NANOS,
write: 100_000 * constants::WEIGHT_PER_NANOS,

polkadot weights (at block 9643856, by parity) are:

read: 20_499 * constants::WEIGHT_PER_NANOS,
write: 83_471 * constants::WEIGHT_PER_NANOS,

polkadot weights (at block 10966052, by our infrastructure) are:

read: 26_527 * constants::WEIGHT_PER_NANOS,
write: 99_766 * constants::WEIGHT_PER_NANOS,

• Weights where only added to spiritnet. Not sure if we need them for peregrine too.
• multiplied with 1.1 since polkadot does the same
  • when the DB grows the weight also gets heavier.
  • 1.1 should cover the weight increase until the next release

TODO

• [ ] ⚠️ reads got twice as expensive
• [x] run benchmark on benchmark server

Checklist:

• [ ] I have verified that the code works
  • [ ] No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• [ ] I have verified that the code is easy to understand
  • [ ] If not, I have left a well-balanced amount of inline comments
• [ ] I have left the code in a better state
• [ ] I have documented the changes (where applicable)