Categorize admin settings sidebar panel (#26030)

This PR reorganize and categorize the admin settings sidebar panel into
groups:

- User Accounts, User Emails, Organizations, Authentication Sources ->
Identity & Access
- Repositories, Packages -> Code Assets
- Webhooks, Applications -> Integrations

Before:

<img width="1346" alt="Screen Shot 2023-07-21 at 10 30 28"
src="https://github.com/go-gitea/gitea/assets/17645053/e0c5ae83-464f-4aaa-8bab-2c5258c9278d">

After:

all configurable settings enabled (package, oauth, webhook)

<img width="1153" alt="Screen Shot 2023-07-21 at 10 27 30"
src="https://github.com/go-gitea/gitea/assets/17645053/88acf3f5-0623-4307-8654-69c654d80874">

all configurable settings disabled (package, oauth, webhook)

<img width="1391" alt="Screen Shot 2023-07-21 at 10 25 19"
src="https://github.com/go-gitea/gitea/assets/17645053/9e13aa60-e75c-4077-afd6-3da9e0ae18dd">

only oauth enabled

<img width="1323" alt="Screen Shot 2023-07-21 at 10 26 23"
src="https://github.com/go-gitea/gitea/assets/17645053/ce4f9ec0-b141-4d5e-ac13-46d001724dc5">

only webhook enabled

<img width="1350" alt="Screen Shot 2023-07-21 at 10 26 55"
src="https://github.com/go-gitea/gitea/assets/17645053/702491bd-083e-44fa-82bc-52c4571e54ac">

options/locale/locale_en-US.ini

@@ -2627,10 +2627,13 @@ teams.invite.description = Please click the button below to join the team.
 
 [admin]
 dashboard = Dashboard
+identity_access = Identity & Access
 users = User Accounts
 organizations = Organizations
+assets = Code Assets
 repositories = Repositories
 hooks = Webhooks
+integrations = Integrations
 authentication = Authentication Sources
 emails = User Emails
 config = Configuration