Adjust the order of slowlog'x-opaque-id to avoid being truncated

[t-ming]

Pr#21609 modified the slowlog pattern layout trunactes from the end. And the later Pr#31539 adds a useful field x-opaque-id after source. When the query body is long than 10kB, x-opaque-id will be trunacted. Adjust the order of x-opaque-id to avoid being truncated. And any field added in the future should add before source to avoid being truncated.

[cla-checker-service]

Author of the following commits did not sign a Contributor Agreement:
8a8c9d2

Please, read and sign the above mentioned agreement if you want to contribute to this project

[ghost]

Hi @t-ming, we have found your signature in our records, but it seems like you have signed with a different e-mail than the one used in your Git commit. Can you please add both of these e-mails into your Github profile (they can be hidden), so we can match your e-mails to your Github profile?

[t-ming]

thanks @jasontedor . I added emial but not sure that cla bot will re check it.

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/Logging)

[pgomulka]

@elasticmachine ok to test

[pgomulka]

@t-ming can you please have a look at this test failure?

org.elasticsearch.index.SearchSlowLogTests.testSlowLogSearchContextPrinterToLog