[Improve](streaming-job) support specifying offset for StreamingInsertJob create and alter

[JNSimba]

Summary

• Support specifying offset (binlog position, LSN, named modes) when creating or altering a StreamingInsertJob via FROM MYSQL/POSTGRES path.
• FE: extend DataSourceConfigValidator to validate offset formats (initial/snapshot/latest/earliest/JSON); earliest is MySQL-only, rejected for PostgreSQL. Implement JdbcSourceOffsetProvider.deserializeOffsetProperty() for named modes and JSON offset parsing. Remove S3-only restriction in StreamingInsertJob.initInsertJob() and modifyPropertiesInternal() so CDC jobs can also use offset property. On ALTER, sync offset to sourceProperties for the FROM...TO path.
• BE: support JSON LSN offset {"lsn":"N"} in PostgresSourceReader.generatePostgresConfig(), and handle SPECIFIC_OFFSETS mode in JdbcIncrementalSourceReader.getStartOffsetFromConfig().
• Fix JdbcOffset.isValidOffset() and toSerializedJson() to return meaningful values instead of hardcoded false/null.

Test plan

• Regression test: test_streaming_mysql_job_special_offset — earliest/latest/JSON binlog offset with data sync verification, ALTER JOB offset change, invalid format rejection
• Regression test: test_streaming_postgres_job_special_offset — initial/latest with data sync, ALTER JOB with JSON LSN offset and data sync verification, earliest rejection for PG, invalid format rejection
• Regression test: test_streaming_mysql_job_special_offset_restart_fe — create job with JSON binlog offset, verify data sync, restart FE, verify job recovery and continued sync

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[Thearas]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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[JNSimba]

run buildall