prepare for default branch renaming

[mshustov]

In other integrations repositories, we use the convention with main as the default branch name.

[loyd]

In other integrations repositories

Which integrations?

[slvrtrn]

Which integrations?

E.g., https://github.com/ClickHouse/clickhouse-go https://github.com/ClickHouse/clickhouse-connect https://github.com/ClickHouse/clickhouse-java https://github.com/ClickHouse/clickhouse-js

[loyd]

I see the point of consistency, but you have some unique integrations.

I'm not against renaming the main branch (although I have many local commands that depend on master naming and am not a fan of master->main global renaming (bikeshedding); it is such a pain).