Add more information when a fetch fails

[leanmendoza]

In this block of code https://github.com/decentraland/builder-client/blob/main/src/client/BuilderClient.ts#L102

    try {
      upsertResponse = await this.fetch(`/v1/items/${item.id}`, {
        headers: { 'content-type': 'application/json' },
        body: JSON.stringify({
          item: { ...item, eth_address: this.getAddress() }
        }),
        method: 'put'
      })
      upsertResponseBody =
        (await upsertResponse.json()) as ServerResponse<RemoteItem>
    } catch (error) {
      throw new ClientError(error.message, undefined, null)
    }

If the fetch fails gracefully and there is no body, it's anyway trying to call the .json(). This always force the error to Unexpected token < in JSON at position 0 and throw away the useful data to know what is happen (for example a Forbidden status code)

[LautaroPetaccio]

In order to fix this issue, the upsertResponse found here must be checked before trying to get its JSON body.