Use Merkle trees in ACE

[pct960]

This PR introduces the use of Merkle trees in table-diff with mtree-diff. Furthermore, it also adds several optimisations to regular table-diff to enable it to run on medium-sized tables. To use this feature:

1. Initialise the Merkle tree objects using:

   ./pgedge ace mtree build <cluster> <schema>.<table> --max-cpu-ratio=1 --analyse=true --recreate-objects=true
   

   --analyse=true can be very time-consuming depending on the size of the table. It's recommended to manually perform an ANALYZE <table> in Postgres and avoid using this flag.

2. Diff can be performed using:

   ./pgedge ace mtree diff <cluster> <schema>.<table> --max-cpu-ratio=1
   

   Performing an mtree-diff automatically updates the Merkle tree before performing the diff. It's also possible to separately update the trees using:

   ./pgedge ace mtree update <cluster> <schema>.<table> --rebalance=true
   

   --rebalance=true will perform splits and merges of blocks based on changes in the underlying keyspace. It's not necessary to perform rebalancing unless it's essential. The default update operation in mtree-diff takes care of block splits and updates but defers merges. This is to preserve parent-child relationships and avoid costly recursions due to merged blocks.

[mmols]

Functionality worked well for me - although I exercised it on a very small table. Great work

My feedback is mostly around documentation / presentation.