fix(oauth): dont convert config values to string when building consent url

[pedroslopez]

What

Fixes OC issue https://github.com/airbytehq/oncall/issues/1250

If the configuration passed to generate the consent URL includes non-string values, they would be implicitly converted to strings when replacing masked values with secrets.

We noticed this happening specifically for Salesforce when re-authenticating the source, since it uses the is_sandbox field, which is a boolean. Issuing the get_consent_url call for an already created connector would return a 422 status code with the following error:

io.airbyte.validation.json.JsonValidationException: json schema validation failed when comparing the data to the json schema. 
Errors: $.is_sandbox: string found, boolean expected 
Schema: 
{
  "type" : "object",
  "properties" : {
    "is_sandbox" : {
      "type" : "boolean",
      "path_in_connector_config" : [ "is_sandbox" ]
    }
  },
  "additionalProperties" : false
}

How

The getOAuthFromDBIfNeeded method was using a string map and calling Jsons.deserializeToStringMap, which basically converts all values to strings. In order to keep the original types, I reworked the implementation to use JsonNodes directly.

[pedroslopez]

I noticed this, but it's not an new issue, just commented in case it comes up sometime in the future. I verified with the previous behavior and if there was a nested object in the input configuration, deserializeToStringMap actually threw an error.