[Enhancement] Do some code optimization.[MessageEntity]

[Alonexc]

Search before asking

• I had searched in the issues and found no similar issues.

Enhancement Request

located at:
eventmesh-storage-plugin/eventmesh-storage-standalone/src/main/java/org/apache/eventmesh/storage/standalone/broker/model/MessageEntity.java
analysis and explanation:
a. 'MessageEntity' does not define a 'serialVersionUID' field
b. Make "message" transient or serializable.

Describe the solution you'd like

a. add serialVersionUID
b. add transient

Are you willing to submit PR?

• Yes I am willing to submit a PR!

[jevinjiang]

Can I work on this issue? kindly assign it to me!