oauth: add oauth_client_id and oauth_client_secret to connectors

[mdibaiee]

• Adds oauth_client_id and oauth_client_secret to connectors table
• Revokes select access on the table as a whole, and grants select on all columns except oauth_client_secret to authenticated role
• Adds functions that allow the UI to generate an Authorization URL for a connector as well as generating the access token once we have code and state
• Adds a function that can be used to encrypt the spec of the connector, with the intention of adding client_id and client_secret to the spec before encryption.
• Agent now updates connectors table with oauth2_spec of the connector

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This change is 

[mdibaiee]

Added a new operation encrypt-config which allows the frontend to send encryption requests, with the difference that this function will add credentials/client_id and credentials/client_secret to the spec before sending it to encryption service. (cc @jgraettinger @travjenkins @psFried)

It can be called like so:

curl -i --location --request POST 'http://localhost:5431/functions/v1/' \
   --header 'Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJzdXBhYmFzZS1kZW1vIiwicm9sZSI6ImFub24ifQ.625_WdcF3KHqz5amU0x2X5WWHP-OEs_4qj0ssLNHzTs' \
   --header 'Content-Type: application/json' \
   --data @request.json

If the client_id and client_secret are in any way exposed in the response of the encryption service, this function will avoid sending them back to client and will error instead. Try it by removing secret: true from either client_id or client_secret.

request.json:

{
  "operation": "encrypt-config",
  "connector_id": "06:ab:80:41:d8:00:5c:00",
  "config": {"credentials": {}, "greetings": 10},
  "schema": {
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "Test Source Spec",
    "type": "object",
    "required": [
      "greetings"
    ],
    "properties": {
      "credentials": {
        "title": "Authentication",
        "description": "Google API Credentials",
        "type": "object",
        "required": [
          "client_id",
          "client_secret"
        ],
        "properties": {
          "client_id": {
            "title": "Client ID",
            "type": "string",
            "secret": true
          },
          "client_secret": {
            "title": "Client Secret",
            "type": "string",
            "secret": true
          },
          "refresh_token": {
            "title": "Refresh Token",
            "type": "string",
            "secret": true
          }
        },
        "x-oauth2-provider": "google"
      },
      "greetings": {
        "title": "Number of Greetings",
        "description": "Number of greeting documents to produce when running in non-tailing mode",
        "default": 1000,
        "type": "integer"
      }
    }
  }
}