Changed image of openid-connect logo for better look on arc-green theme (#11312)

* Set background of openIDConnect logo to white in arc-green theme

* Fixed linting off arc-green theme

Signed-off-by: Leo Maroni <git@em0lar.de>

* Revert changes of first commit (white background) and replaced the image

* Updated openid_connect (part 2)

* Update public/img/auth/openid_connect.svg

Now in one line

Co-authored-by: silverwind <me@silverwind.io>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

docs/content/doc/advanced/cmd-embedded.en-us.md

@@ -54,7 +54,7 @@ Listing all embedded files with `openid` in their path:
 
 ```
 $ gitea embedded list '**openid**'
-public/img/auth/openid_connect.png
+public/img/auth/openid_connect.svg
 public/img/openid-16x16.png
 templates/user/auth/finalize_openid.tmpl
 templates/user/auth/signin_openid.tmpl

models/oauth2.go

@@ -41,7 +41,7 @@ var OAuth2Providers = map[string]OAuth2Provider{
 		},
 	},
 	"gplus":         {Name: "gplus", DisplayName: "Google", Image: "/img/auth/google.png"},
-	"openidConnect": {Name: "openidConnect", DisplayName: "OpenID Connect", Image: "/img/auth/openid_connect.png"},
+	"openidConnect": {Name: "openidConnect", DisplayName: "OpenID Connect", Image: "/img/auth/openid_connect.svg"},
 	"twitter":       {Name: "twitter", DisplayName: "Twitter", Image: "/img/auth/twitter.png"},
 	"discord":       {Name: "discord", DisplayName: "Discord", Image: "/img/auth/discord.png"},
 	"gitea": {Name: "gitea", DisplayName: "Gitea", Image: "/img/auth/gitea.png",