Add ai_gateway_timeout_seconds column in ai_settings table

What does this MR do and why?

• Add new column ai_gateway_timeout_seconds in ai_settings table with a default value of 60 seconds.
• Update the duoUpdateSettings mutation to accept this new field.

References

Add new column in `ai_settings` table (#579182) Bug issue: Make 60s timeout applied by AIGW when making re... (#567878)

Screenshots or screen recordings

How to set up and validate locally

• Add following mutation to GraphQL explorer

mutation updateDuoSettings($input: DuoSettingsUpdateInput!) {
  duoSettingsUpdate(input: $input) {
    errors
    __typename
  }
}

# variables:

{
  "input":{
    "aiGatewayTimeoutSeconds": 30
  }
}

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