* Extrinsic for reserving a parachain ID

* Fixes

* Fixes

* Docs

* cargo run --release --features=runtime-benchmarks -- benchmark --chain=westend-dev --steps=50 --repeat=20 --pallet=runtime_common::paras_registrar --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --header=./file_header.txt --output=./runtime/westend/src/weights/runtime_common_paras_registrar.rs

* Update runtime/common/src/paras_registrar.rs

Co-authored-by: Robert Habermeier <[email protected]>

* cargo run --release --features=runtime-benchmarks -- benchmark --chain=kusama-dev --steps=50 --repeat=20 --pallet=runtime_common::paras_registrar --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --header=./file_header.txt --output=./runtime/kusama/src/weights/runtime_common_paras_registrar.rs

Co-authored-by: Parity Bot <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Robert Habermeier <[email protected]>