feat: add support for processing of upload_v2 job type by slave

[shekhar-rudder]

Description

Master

• Added some logs in loadfiles.go
• Now setting status for staging files to succeeded in loadfiles.go for the integration tests to pass
• I had missed one SQL query which was using staging_file_id to query load files. Created a new function getLoadFilesMetadataQuery to query based on either upload_id or staging_file_id based on a env flag

Notifier

• Made JobTypeUploadV2 a valid job type

Slave

• We now have 2 methods - processStagingFile and processMultiStagingFiles for v1 and v2 jobs respectively. Both internally call processSingleStagingFile whose job is to download the stagingfile and read it to create load files.
• There are two payload types - payload and payload sharing basePayload for common fields
• Since a jobRun struct can have multiple staging files, removed stagingFilePath and stagingFileReader and replaced it with a list of staging file processors stagingFileProcessors
• Added tableWriterMutexes to prevent concurrent writes to the same table
• Added mutex for outputFileWritersMap and tableEventCountMap since they can now be accessed concurrently
• Now that a job can have multiple staging files, introduce a config maxConcurrentStagingFiles to control number of staging files being processed concurrently

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.