openapi: Change schema for thread ids to string

[pavog]

The schema for the thread IDs in /threads is currently defined as:

schema:
  type: array
  items:
    type: string
  example: "[\"AABBCCDD\", \"EEFFGGHH\"]"

this is wrong.
It would mean that my request to fetch multiple threads would look like this:
https://api.modrinth.com/v2/threads?ids=vNcGR3Fd&ids=EBqEP7Kk
This does not work and returns this response:

{
  "error": "invalid_input",
  "description": "Error while validating input: Query deserialize error: duplicate field `ids`"
}

This PR changes the schema for the thread IDs to string.
It is actually a string, written like an array in json.

New

schema:
 type: string
 example: "[\"AABBCCDD\", \"EEFFGGHH\"]"

And the request will look like this:
https://api.modrinth.com/v2/threads?ids=["vNcGR3Fd", "EBqEP7Kk"]

Related to:

• openapi: Change schema for MultipleProjectIdentifier to string #138
• openapi: Change schema type for loaders and game_versions to string #139
• openapi: Change schema for user ids to string #140
• openapi: Change schema for notification ids to string #141
• openapi: Change schema for report ids to string #142