Implement CSR_DENSITY and/or CSR_LEAVE_GAPS options

[adsharma]

A 160MB parquet rel table from livejournal results in 500MB in native rel tables.

Half of it is due to bi-directional storage which can be optimized via STORAGE_DIRECTION='FWD'

Status today:

• CSR density is hard-coded:
• PACKED_CSR_DENSITY = 0.8
• no table option
• PackedCSRInfo even has a TODO saying it should be serialized/configured per node group.

The task is to make them configurable and use for read-only tables.