Support customized header in Rest catalog client

[flyrain]

Java and Python clients support customized http header. Rust client needs to support that as well.

Here is a Java client configuration example:

--conf spark.sql.catalog.rest.header.X-CUSTOMIZED-HEADER=default

Here is a Python config example:

catalog:
  default:
    uri: http://localhost:8082/
    header.X-CUSTOMIZED-HEADER: default

cc @Fokko @RussellSpitzer @liurenjie1024 @himadripal

[whynick1]

@flyrain if nobody is already looking at this, would love to try and take a stab at this?

[flyrain]

Assigned to you. Thanks for taking a look!