Cosmos: Add config validations to ensure GraphQL types are either entity names or singular types

[Aniruddh25]

Today, both the runtime configuration and the GraphQL schema are provided by the customer. For the engine, to behave correctly, the types specified in the GraphQL schema here:

data-api-builder/src/Service/schema.gql

Line 9 in d5820d4

type Planet @model(name:"Planet"){

should match either

1. the entity name in the runtime configuration see this:

   data-api-builder/src/Service/dab-config.Cosmos.json

   Line 34 in d5820d4

   "Planet": {

   
   or
2. the graphql.type.singular property of the entity:

   data-api-builder/src/Service/dab-config.Cosmos.json

   Line 39 in d5820d4

   "singular": "Planet",

It is quite possible to have configuration errors, where the schema doesn't match the configuration. This issue is to add validations at startup to make sure these errors are easily found and a useful error is given to the developer to correct their configuration as per the graphql schema.
E.g. of someone who already encounter this: #876