Handle filter_current_dashboard on update

[mbazhlekova]

Description

This PR handles filter_current_dashboard properly on dashboard update. Before it was only handled on dashboard create.

Fixes #1494

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My commit message follows conventional commits
• My code is formatted to Go standards
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes. Go here for instructions on running tests locally.

How to test this change?

Please describe how to test your changes. Include any relevant steps in the UI, HCL file(s), commands, etc

1. Create a dashboard resource with the following HCL file

resource "newrelic_one_dashboard" "default" {
  name        = "Ticket 1494"
  description = "Managed via Terraform"

  page {
    name        = "Simple Page"
    description = "Simple Page"

    # Pie charts
    widget_pie {
      title                    = "Filter Example"
      row                      = 1
      column                   = 1
      width                    = 5
      height                   = 5
      linked_entity_guids      = null
      filter_current_dashboard = true
      nrql_query {
        query = "FROM K8sClusterSample select uniqueCount(hostname) FACET clusterName limit max since 5 minutes ago"
      }
    }

    widget_pie {
      title                    = "Target Example"
      row                      = 1
      column                   = 6
      width                    = 7
      height                   = 5
      linked_entity_guids      = null
      filter_current_dashboard = false
      nrql_query {
        query = "FROM K8sClusterSample select uniqueCount(hostname) FACET instanceType limit max since 5 minutes ago"
      }
    }
  }
}

2. Run terraform plan and terraform apply
3. Navigate to created dashboard in New Relic
4. Go to edit the Filter Example widget and verify that Filter the current dashboard is selected
5. Go back to Terraform and set filter_current_dashboard to false
6. Run terraform plan and terraform apply again
7. Go to edit the Filter Example widget and verify that Filter the current dashboard is no longer selected

[ChandraIragavarapu]

looks good.
Discussed with the team and few improvement points to be consider in future:

1. Use proper index looping counters instead of single char like i,j...
2. Use functions when we have complex logic. For example in file 'structures_newrelic_one_dashboard.go' around line 904