[Offload] Make the field name in `OffloadPolicies` match with config file (#8310)

Fixes #8220 

### Motivation

Currently, the fields' values couldn't be set properly by the Pulsar broker config file(`broker.conf` or `standalone.conf`). 

### Modifications

changed fields in `OffloadPolicies`

1. managedLedgerOffloadAutoTriggerSizeThresholdBytes
2. managedLedgerOffloadDeletionLagMs
1 file changed
tree: dc6c8e1c45bed18990251d8447fc880f3c28929c
  1. distribution/
  2. docker/
  3. tests/