sql: change `system.table_statistics` to honor fine grained data domiciliation rules over indexed data

[knz]

Describe the problem

The table statistics stored in system.table_statistics contain a copy of table data in the histogram column.

When the data from the table is constrained to certain regions (data domiciliation), the table system.table_statistics is not constrained and thus the data "escapes" the region it should remain at.

This makes it impossible to do strict data sovereignty partitioning using multi-region CockroachDB when domicilied data is indexed. (The issue does not exist when domicilied data is not indexed.)

Note: we already document this limitation in https://www.cockroachlabs.com/docs/stable/data-domiciling.html#limitations

Epic: CRDB-10287

To Reproduce

1. create a multi-region table
2. populate indexed data in each region
3. create statistics for that table
4. read the content of system.table_statistics and observe data from regions duplicated in the histogram column

Expected behavior

The table system.table_statistics should be split into different ranges so that the stats for each table are stored in the same region as the data that's constrained by zone configs.

Environment:

crdb v21.2

Jira issue: CRDB-10286

[knz]

cc @awoods187 you may want to track this for GDPR compliance

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