feat: implement builder pattern for CustomOpPayloadBuilder

[varun-doshi]

📝 Summary

Implement proposer Builder pattern for CustomOpPayloadBuilder

💡 Motivation and Context

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Closes #504
To implement proposer Builder pattern for CustomOpPayloadBuilder

✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[SozinM]

@varun-doshi thanks! this is going in the right direction.

1. There is 2 places when we build CustomOpPayloadBuilder - payload_builder_vanilla.rs and payload_builder.rs
2. I was thinking of creating unified builder for both of them, call it like CustomOpPayloadBuilderBuilder and make all fields as optional
3. Then we could build one or the other, depending on the feature
   that would be a good start imo

[varun-doshi]

Got it...will make appropriate changes

[SozinM]

@ferranbt take a look at this pls