Display RequestMetadata that's part of ActionCache entries

This makes it possible to see the build tool's invocation ID and version
number on action and uncached action result pages. This feature will
become a lot more interesting once the following API for remote-apis
lands:

bazelbuild/remote-apis#186

Once we have that, we can display Bazel target names, configuration IDs,
etc., meaning we can finally correlate Build Event Stream events with
individual actions in Buildbarn.

cmd/bb_browser/main.go

@@ -8,6 +8,7 @@ import (
 	"path"
 	"time"
 
+	remoteexecution "github.com/bazelbuild/remote-apis/build/bazel/remote/execution/v2"
 	"github.com/buildbarn/bb-browser/pkg/proto/configuration/bb_browser"
 	"github.com/buildbarn/bb-remote-execution/pkg/proto/resourceusage"
 	blobstore_configuration "github.com/buildbarn/bb-storage/pkg/blobstore/configuration"
@@ -98,6 +99,13 @@ func main() {
 			}
 			return &pb
 		},
+		"to_request_metadata": func(any *any.Any) *remoteexecution.RequestMetadata {
+			var pb remoteexecution.RequestMetadata
+			if ptypes.UnmarshalAny(any, &pb) != nil {
+				return nil
+			}
+			return &pb
+		},
 		"shellquote": shellquote.Join,
 		"timestamp_rfc3339": func(t time.Time) string {
 			// Converts a timestamp to RFC3339 format.

cmd/bb_browser/templates/page_action.html

@@ -166,6 +166,26 @@ <h2 class="my-4">Execution metadata</h2>
 	</table>
 
 	{{range .AuxiliaryMetadata}}
+		{{with to_request_metadata .}}
+			<h3 class="my-4">Request metadata</h3>
+			<table class="table" style="table-layout: fixed">
+				{{with .ToolDetails}}
+					<tr>
+						<th style="width: 25%">Tool:</th>
+						<td style="width: 75%">{{.ToolName}} {{.ToolVersion}}</td>
+					</tr>
+				{{end}}
+				<tr>
+					<th style="width: 25%">Tool invocation ID:</th>
+					<td class="text-monospace" style="width: 75%">{{.ToolInvocationId}}</td>
+				</tr>
+				<tr>
+					<th style="width: 25%">Correlated invocations ID:</th>
+					<td class="text-monospace" style="width: 75%">{{.CorrelatedInvocationsId}}</td>
+				</tr>
+			</table>
+		{{end}}
+
 		{{with to_file_pool_resource_usage .}}
 			<h3 class="my-4">File pool resource usage</h3>
 			<table class="table" style="table-layout: fixed">