RFC. Slightly better persistency in clickhouse-local

[alexey-milovidov]

1. It should use Atomic database engine instead of Memory for the default database, so the metadata will be preserved across runs.
2. The default database should be named default instead of _local.
3. It should use ./clickhouse directory as the working directory instead of a random directory in /tmp
4. Nevertheless, if the directory cannot be created, it should continue working.
5. Temporary tables for File IO should use the mechanism of the temporary tables.
6. Ideally, it should not create any directories if the queries are purely stateless like SELECT 1.

[Algunenano]

I use clickhouse-local all the time to test temporary things that I want to go away on exit (things like #50628 (comment) for example). So it'd be great to keep the temporary behaviour as an option if possible (clickhouse local --temp / clickhouse local --persist ?)

No strong opinion about the other things

[alexey-milovidov]

One idea for clickhouse-local:

• use default database as default;
• make it Atomic instead of Memory;
• but avoid creating any files unless the first table is created;
• when we create tables implicitly for the inputs, instead of normal tables, create them as temporary tables with an engine - in this way, we will avoid creating the database files in most cases.

Bonus: the support for EXCHANGE, CREATE OR REPLACE, etc.