Ignore sharding_key_id column on runner models

What does this MR do and why?

This MR:

1. marks sharding_key_id column as ignored in the models
2. drops check constraints for sharding_key_id on runner tables
3. removes all usages of the sharding_key_id columns in the runner tables

NOTE: This MR is best reviewed commit-by-commit.

References

• Ignore sharding_key_id column in runner models (#547654 - closed)
• Remove sharding_key_id usages from runner-relat... (#523853 - closed)
• Remove logic keeping sharding_key_id up to date... (#530294 - closed)
• Follow-up from "POC: Move partition_id to token... (#524364 - closed)

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