(GH-70) Implemented validation for tags being supplied

docs/input/docs/rules/choco0013.md

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+---
+Title: Tags Are Missing
+Description:
+Category: Requirements
+---
+
+:::{.alert .alert-warning}
+**Preliminary Notice**
+This rule is not yet available in chocolatey-vscode.
+It is a planned rule for 0.8.0.
+:::
+
+## Issue
+
+In the nuspec, there is a `<tags />` element. It was found to be missing or empty in the package. 
+
+## Recommended Solution
+
+Please update the nuspec to include a `<tags />` element that is non-empty. If your nuspec file is missing this field, you should run the `Chocolatey: Create new Chocolatey package` with the default template and look at the output from that (ensure you have the [latest version of Chocolatey](https://chocolatey.org/packages?q=id%3Achocolatey)).
+
+## Reasoning
+
+Tags aid in categorization of packages and underlying software. Tags should be relevant to the software that is being installed. It will give folks more options when searching for particular software on the site and may turn up in results it may have not otherwise came up in.
+
+## See also
+
+- [Package validator rule](https://github.com/chocolatey/package-validator/wiki/TagsNotEmpty){target = _blank}

src/Chocolatey.Language.Server/Validations/TagsNotEmpty.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Chocolatey.Language.Server.Models;
+using OmniSharp.Extensions.LanguageServer.Protocol.Models;
+
+namespace Chocolatey.Language.Server.Validations
+{
+    /// <summary>
+    ///   Handler to validate that no tags contain a comma.
+    /// </summary>
+    /// <seealso href="https://github.com/chocolatey/package-validator/blob/master/src/chocolatey.package.validator/infrastructure.app/rules/TagsAreSpaceSeparatedRequirement.cs">Package validator comma separated tags validation rule.</seealso>
+    public sealed class TagsNotEmpty : NuspecRuleBase
+    {
+        private const string VALIDATION_MESSAGE = "Tags (tags) are space separated values for referencing categories for software. " +
+                                                  "Please include tags in the nuspec as space separated values";
+
+        public override string Id => "choco0013";
+
+        public override string DocumentationUrl => $"https://gep13.github.io/chocolatey-vscode/docs/rules/{Id}";
+
+        public override ValidationType ValidationType => ValidationType.Requirement;
+
+        public override IEnumerable<Diagnostic> Validate(Package package)
+        {
+            if (!package.Tags.Any() || package.Tags.All(t => string.IsNullOrWhiteSpace(t)))
+            {
+                yield return CreateDiagnostic(package, VALIDATION_MESSAGE);
+            }
+        }
+    }
+}