- allow put custom jar in `${DORIS_HOME}/lib/java_extensions/custom_extension` such as `paimon-s3-0.4.0-incubating.jar`
- add some note for paimon and fqdn
- allow put custom jar in `${DORIS_HOME}/lib/java_extensions/custom_extension` such as `paimon-s3-0.4.0-incubating.jar`
- add some note for paimon and fqdn