Switch some png images to svg versions

These are much smaller in size and scale on all devices better.

Author: khalidabuhakmeh

src/content/docs/identityserver/fundamentals/users.md

@@ -48,7 +48,7 @@ It is very important that you understand how it works when building the login pa
 Recall the diagram showing the relationship of your custom UI pages and the IdentityServer middleware in your
 IdentityServer host application:
 
-![middleware diagram](../overview/images/middleware.png)
+![middleware diagram](../overview/images/middleware.svg)
 
 When your IdentityServer receives an authorize request, it will inspect it for a current authentication session for a
 user. This authentication session is based on ASP.NET Core's authentication system and is ultimately determined by a

src/content/docs/identityserver/overview/big-picture.md

@@ -12,7 +12,7 @@ redirect_from:
 
 Most modern applications look more or less like this:
 
-![an architecture diagram for modern applications with clients and services](./images/appArch.png)
+![an architecture diagram for modern applications with clients and services](./images/application-architecture.svg)
 
 The most common interactions are:
 
@@ -31,7 +31,7 @@ across those applications and endpoints.
 
 Restructuring the application to support a security token service leads to the following architecture and protocols:
 
-![an architecture diagram showing where OAuth 2.0 is used](./images/protocols.png)
+![an architecture diagram showing where OAuth 2.0 is used](./images/protocols.svg)
 
 Such a design divides security concerns into two parts:
 
@@ -78,7 +78,7 @@ depending on your needs)
 and add the IdentityServer middleware to that application. The middleware adds the necessary protocol heads to the
 application so that clients can talk to it using those standard protocols.
 
-![IdentityServer middleware diagram and its relatinship in the ASP.NET Core pipeline](./images/middleware.png)
+![IdentityServer middleware diagram and its relatinship in the ASP.NET Core pipeline](./images/middleware.svg)
 
 The hosting application can be as complex as you want, but we typically recommend to keep the attack surface as small as
 possible by including

src/content/docs/identityserver/overview/images/application-architecture.svg

@@ -12,7 +12,7 @@ redirect_from:
 
 The specs, documentation and object model use a certain terminology that you should be aware of.
 
-![a basic diagrams showing the relationship between users, clients, identityserver, and resources](./images/terminology.png)
+![a basic diagrams showing the relationship between users, clients, identityserver, and resources](./images/terminology.svg)
 
 ## Duende IdentityServer