Create indexing status endpoint

[tk-o]

Create GET /api/indexing-status endpoint.

This task requires representing the IndexingStatus data model in two ways:

• business-level data model, in which we use the best-suiting data types, for example:
  • uses Map type to manage key-value relationships between object s(such as number for chain ID and ChainStatus for the chain-specific indexing status
  • chain IDs are always represented with the number type,
  • date values are represented with the Date type,
  • bigint values are represented with the BigInt type.
• serialized data model
  • must be a 100% compatible input for JSON.stringify
  • must enable deserialization into its buinsess-level data model counterpart

Deserialization must enforce all required validation and invariants enforcement (using Zod).

Checklist:

• All possible permutations of indexing status described in this spreadsheet must be expressed in code including invariants enforcement
• ...

Replaces #834