feat(application): define schema for storage flag in application reso…

…urce

This commit extends the application schema to support the storage flag in the Terraform provider for Juju.
The schema now includes varios attributes for configuring the storage constraints of a Juju application.

docs/resources/application.md

@@ -78,6 +78,7 @@ resource "juju_application" "placement_example" {
 		  latest revision.
 	    * If the charm revision or channel are not updated, then no changes will take 
 		  place (juju does not have an "un-attach" command for resources).
+- `storage` (Attributes Set) Configure storage constraints for the juju application. (see [below for nested schema](#nestedatt--storage))
 - `trust` (Boolean) Set the trust for the application.
 - `units` (Number) The number of application units to deploy for the charm.
 
@@ -122,6 +123,20 @@ Optional:
 - `endpoints` (String) Expose only the ports that charms have opened for this comma-delimited list of endpoints
 - `spaces` (String) A comma-delimited list of spaces that should be able to access the application ports once exposed.
 
+
+<a id="nestedatt--storage"></a>
+### Nested Schema for `storage`
+
+Required:
+
+- `label` (String) The specific storage option defined in the charm.
+
+Optional:
+
+- `count` (Number) The number of volumes.
+- `pool` (String) Name of the storage pool to use. E.g. ebs on aws.
+- `size` (String) The size of each volume. E.g. 100G.
+
 ## Import
 
 Import is supported using the following syntax:

internal/provider/resource_application.go

@@ -6,6 +6,7 @@ package provider
 import (
 	"context"
 	"fmt"
+	"github.com/hashicorp/terraform-plugin-framework/resource/schema/stringdefault"
 	"strings"
 
 	"github.com/hashicorp/terraform-plugin-framework-validators/listvalidator"
@@ -164,6 +165,55 @@ func (r *applicationResource) Schema(_ context.Context, _ resource.SchemaRequest
 					stringplanmodifier.UseStateForUnknown(),
 				},
 			},
+			"storage": schema.SetNestedAttribute{
+				Description: "Configure storage constraints for the juju application.",
+				Optional:    true,
+				NestedObject: schema.NestedAttributeObject{
+					Attributes: map[string]schema.Attribute{
+						"label": schema.StringAttribute{
+							Description: "The specific storage option defined in the charm.",
+							Required:    true,
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"size": schema.StringAttribute{
+							Description: "The size of each volume. E.g. 100G.",
+							Optional:    true,
+							Computed:    true,
+							Default:     stringdefault.StaticString("1G"),
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"pool": schema.StringAttribute{
+							Description: "Name of the storage pool to use. E.g. ebs on aws.",
+							Optional:    true,
+							PlanModifiers: []planmodifier.String{
+								stringplanmodifier.RequiresReplaceIfConfigured(),
+								stringplanmodifier.UseStateForUnknown(),
+							},
+						},
+						"count": schema.Int64Attribute{
+							Description: "The number of volumes.",
+							Optional:    true,
+							Computed:    true,
+							Default:     int64default.StaticInt64(int64(1)),
+							PlanModifiers: []planmodifier.Int64{
+								int64planmodifier.RequiresReplaceIfConfigured(),
+								int64planmodifier.UseStateForUnknown(),
+							},
+						},
+					},
+				},
+				Validators: []validator.Set{
+					setNestedIsAttributeUniqueValidator{
+						PathExpressions: path.MatchRelative().AtAnySetValue().MergeExpressions(path.MatchRelative().AtName("label")),
+					},
+				},
+			},
 			"trust": schema.BoolAttribute{
 				Description: "Set the trust for the application.",
 				Optional:    true,