Potential API/storage format breaking change

[jiacai2050]

Describe This Problem

When release 1.0, breaking change is not acceptable, so we need to

1. Remove bad design
2. Add compatible method to old format

This issue is mainly used to collect potential breaking changes

Proposal

As above

Additional Context

Some examples I can think of

• SstMetaData's size is 0 after flush #321, we need to record sst file size in manifest;
• feat: correct column order  #340;
• Impose a custom format of SST #495 Define the custom format for SST;

[ShiKaiWi]

What I can come up with now includes:

• Define the custom format for SST (now it is totally a parquet file) for the possible brand-new format in the future;
• Refactor the manifest implementation because current one is complicated and may not work well with OBKV;

[ShiKaiWi]

One more thing deserved mentioning here, currently the protocol maps the tenant to the schema, which is actually unreasonable.

[jiacai2050]

• fix: rename NumKeyColumns to PrimaryKeyIndexes #526

[ShiKaiWi]

#538 tries to reduce the size of the meta data used in manifest, which may help solve the problem:

Refactor the manifest implementation because current one is complicated and may not work well with OBKV;

[ShiKaiWi]

All the breaking changes we know are all finished.