Add support for Multitenancy

[leandrorosa]

The helm chart doesn't provide a way to configure Multitenancy options. It is lacking sharded_tables and sharded_mappings options.

I would like to either be able to reference my own pgdog.toml file or to be able to configure Multitenancy properly.

Ref: https://docs.pgdog.dev/features/multi-tenancy/

[levkk]

Sounds good. If you'd like to submit a PR, I'd be happy to review it. If not, no worries, I'll take a look at this next week!

My preferred approach would be to include both in values.yaml, perhaps following the same list format with use for databases and users.

[leandrorosa]

No worries, I will be happy to submit a PR. Am going to open in the beginning of the next week then.