replace background image (grpc-bg.svg) with a simple gradient (#317)

#316

> The background image (grpc-bg.svg) is significantly large in size
(1.7MB). When embedded into servers with limited bandwidth, it consumes
a significant portion of the available resources and results in slower
load times.
> 
> Please consider replacing the existing image with a simpler pattern or
opt for a plain color background.

Before:

<img width="735" alt="Screenshot 2024-04-27 at 11 29 56 AM"
src="https://github.com/fullstorydev/grpcui/assets/1919660/19d65eb2-38fa-4a42-a2ca-331911766c9d">

After:

<img width="732" alt="Screenshot 2024-04-27 at 11 31 33 AM"
src="https://github.com/fullstorydev/grpcui/assets/1919660/4e89e990-d635-4443-a6e2-1e4628494911">

Any feedback on the exact color choices is welcome.
CC: @lqs

internal/resources/standalone/assets.go

@@ -7,7 +7,7 @@ import (
 
 const IndexTemplateName = "index-template.html"
 
-//go:embed *.html *.css *.png *.js *.svg
+//go:embed *.html *.css *.png *.js
 var res embed.FS
 
 func IndexTemplate() []byte {

internal/resources/standalone/index-template.html

@@ -62,7 +62,7 @@
       margin: 0;
       padding: 32px 24px;
       color: white;
-      background: #186064 url("grpc-bg.svg") no-repeat center/cover;
+      background: linear-gradient(to bottom right, #0C4348, #317178, #5F8C8C)
     }
 
     .heading h1 {

standalone/standalone.go

@@ -54,7 +54,7 @@ func Handler(ch grpcdynamic.Channel, target string, methods []*desc.MethodDescri
 
 	var mux http.ServeMux
 
-	// Add go-bindata resources bundled in standalone package TOC
+	// Add embedded resources bundled in standalone package TOC
 	for _, assetName := range standalone.AssetNames() {
 		// the index file will be handled separately
 		if assetName == standalone.IndexTemplateName {