feat(coderd/healthcheck): add access URL error codes and healthcheck doc (#10915)

Relates to #8965

- Added error codes for separate code paths in health checks
- Prefixed errors and warnings with error code prefixes
- Added a docs page with details on each code, cause and solution

Co-authored-by: Muhammad Atif Ali <atif@coder.com>

coderd/healthcheck/derphealth/derp.go

@@ -136,9 +136,7 @@ func (r *Report) Run(ctx context.Context, opts *ReportOptions) {
 				r.Healthy = false
 			}
 
-			for _, w := range regionReport.Warnings {
-				r.Warnings = append(r.Warnings, fmt.Sprintf("[%s] %s", regionReport.Region.RegionName, w))
-			}
+			r.Warnings = append(r.Warnings, regionReport.Warnings...)
 			mu.Unlock()
 		}()
 	}
@@ -202,9 +200,7 @@ func (r *RegionReport) Run(ctx context.Context) {
 				unhealthyNodes++
 			}
 
-			for _, w := range nodeReport.Warnings {
-				r.Warnings = append(r.Warnings, fmt.Sprintf("[%s] %s", nodeReport.Node.Name, w))
-			}
+			r.Warnings = append(r.Warnings, nodeReport.Warnings...)
 			r.mu.Unlock()
 		}()
 	}
@@ -228,7 +224,7 @@ func (r *RegionReport) Run(ctx context.Context) {
 	} else if unhealthyNodes == 1 {
 		// r.Healthy = true (by default)
 		r.Severity = health.SeverityWarning
-		r.Warnings = append(r.Warnings, oneNodeUnhealthy)
+		r.Warnings = append(r.Warnings, health.Messagef(health.CodeDERPOneNodeUnhealthy, oneNodeUnhealthy))
 	} else if unhealthyNodes > 1 {
 		r.Healthy = false
 
@@ -292,7 +288,7 @@ func (r *NodeReport) Run(ctx context.Context) {
 	}
 
 	if r.UsesWebsocket {
-		r.Warnings = append(r.Warnings, warningNodeUsesWebsocket)
+		r.Warnings = append(r.Warnings, health.Messagef(health.CodeDERPNodeUsesWebsocket, warningNodeUsesWebsocket))
 		r.Severity = health.SeverityWarning
 	}
 }