[PM-17562] Update documentation for event integrations (#5924)

* [PM-17562] Update documentation for event integrations

* Fix SonarQube suggestion, bring ASB event listener in line with integration listener

* Apply suggestions from code review

Co-authored-by: Matt Bishop <mbishop@bitwarden.com>

* Updates to README - PR fixes, additional context, tense alignment

* Fix the formatting for inlined code snippets

* Add links to different sections; remove inline code formatting in favor of single bacticks for JSON

---------

Co-authored-by: Matt Bishop <mbishop@bitwarden.com>

test/Core.Test/AdminConsole/Models/Data/EventIntegrations/IntegrationMessageTests.cs

@@ -0,0 +1,85 @@
+using System.Text.Json;
+using Bit.Core.AdminConsole.Models.Data.EventIntegrations;
+using Bit.Core.Enums;
+using Xunit;
+
+namespace Bit.Core.Test.Models.Data.EventIntegrations;
+
+public class IntegrationMessageTests
+{
+    private const string _messageId = "TestMessageId";
+
+    [Fact]
+    public void ApplyRetry_IncrementsRetryCountAndSetsDelayUntilDate()
+    {
+        var message = new IntegrationMessage<WebhookIntegrationConfigurationDetails>
+        {
+            Configuration = new WebhookIntegrationConfigurationDetails("https://localhost"),
+            MessageId = _messageId,
+            RetryCount = 2,
+            RenderedTemplate = string.Empty,
+            DelayUntilDate = null
+        };
+
+        var baseline = DateTime.UtcNow;
+        message.ApplyRetry(baseline);
+
+        Assert.Equal(3, message.RetryCount);
+        Assert.NotNull(message.DelayUntilDate);
+        Assert.True(message.DelayUntilDate > baseline);
+    }
+
+    [Fact]
+    public void FromToJson_SerializesCorrectly()
+    {
+        var message = new IntegrationMessage<WebhookIntegrationConfigurationDetails>
+        {
+            Configuration = new WebhookIntegrationConfigurationDetails("https://localhost"),
+            MessageId = _messageId,
+            RenderedTemplate = "This is the message",
+            IntegrationType = IntegrationType.Webhook,
+            RetryCount = 2,
+            DelayUntilDate = DateTime.UtcNow
+        };
+
+        var json = message.ToJson();
+        var result = IntegrationMessage<WebhookIntegrationConfigurationDetails>.FromJson(json);
+
+        Assert.NotNull(result);
+        Assert.Equal(message.Configuration, result.Configuration);
+        Assert.Equal(message.MessageId, result.MessageId);
+        Assert.Equal(message.RenderedTemplate, result.RenderedTemplate);
+        Assert.Equal(message.IntegrationType, result.IntegrationType);
+        Assert.Equal(message.RetryCount, result.RetryCount);
+        Assert.Equal(message.DelayUntilDate, result.DelayUntilDate);
+    }
+
+    [Fact]
+    public void FromJson_InvalidJson_ThrowsJsonException()
+    {
+        var json = "{ Invalid JSON";
+        Assert.Throws<JsonException>(() => IntegrationMessage<WebhookIntegrationConfigurationDetails>.FromJson(json));
+    }
+
+    [Fact]
+    public void ToJson_BaseIntegrationMessage_DeserializesCorrectly()
+    {
+        var message = new IntegrationMessage
+        {
+            MessageId = _messageId,
+            RenderedTemplate = "This is the message",
+            IntegrationType = IntegrationType.Webhook,
+            RetryCount = 2,
+            DelayUntilDate = DateTime.UtcNow
+        };
+
+        var json = message.ToJson();
+        var result = JsonSerializer.Deserialize<IntegrationMessage>(json);
+
+        Assert.Equal(message.MessageId, result.MessageId);
+        Assert.Equal(message.RenderedTemplate, result.RenderedTemplate);
+        Assert.Equal(message.IntegrationType, result.IntegrationType);
+        Assert.Equal(message.RetryCount, result.RetryCount);
+        Assert.Equal(message.DelayUntilDate, result.DelayUntilDate);
+    }
+}