[Enhancement] Substitution of constants [HttpProtocolAdaptor]

[Alonexc]

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Enhancement Request

Describe the solution you'd like

Located at:eventmesh-protocol-http/src/main/java/org/apache/eventmesh/protocol/http/HttpProtocolAdaptor Replace the constants in the image with the ones in protocol/http/HttpProtocolConstant and remove the unused code from the image.

Note: This issue is only for contributors who have not contributed to eventmesh and want to contribute to eventmesh, and can only be claimed once per contributor!

Are you willing to submit PR?

• [ ] Yes I am willing to submit a PR!