Add omni bencher & chain-spec-builder bins to release (#4557)

Closes: https://github.com/paritytech/polkadot-sdk/issues/4354

This PR adds the steps to build and attach `frame-omni-bencher` and
`chain-spec-builder` binaries to the release draft

## TODO
- [x] add also chain-spec-builder binary
- [ ] ~~check/investigate Kian's comment: `chain spec builder. Ideally I
want it to match the version of the sp-genesis-builder crate`~~ see
[comment](https://github.com/paritytech/polkadot-sdk/pull/4518#issuecomment-2134731355)
- [ ] Backport to `polkadot-sdk@1.11` release, so we can use it for next
fellows release: https://github.com/polkadot-fellows/runtimes/pull/324
- [ ] Backport to `polkadot-sdk@1.12` release

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Co-authored-by: Branislav Kontur <bkontur@gmail.com>