Remove changelog references from docs (#13987)

The `apps/changelog` directory and all its contents were removed,
following its migration to a separate repository. This included the
application's source code, Next.js configurations, Prisma schema and
migrations, public assets, and various client-side React components.

Associated local file references were also cleaned up:
* In `.eslintignore`, the `apps/changelog` entry was removed to prevent
linting the non-existent directory.
* The `tsconfig.json` file was updated by removing `"apps/changelog"`
from its `exclude` array, ensuring the TypeScript compiler no longer
attempts to process the migrated application's files.

These changes ensure the docs repository is free of the migrated
changelog application and its local dependencies.

The changelog repository is now at
https://github.com/getsentry/sentry-changelog

---------

Co-authored-by: Cursor Agent <[email protected]>

Author: dcramer

.eslintignore

@@ -1,2 +1 @@
 .babelrc.js
-apps/changelog

CONTRIBUTING.md

@@ -20,29 +20,3 @@ yarn dev:developer-docs
 ```
 
 With that, the repo is fully set up and you are ready to open local docs under http://localhost:3000
-
-### Database
-
-There is a compose file to start a local postgres db:
-
-```
-docker-compose up -d
-```
-
-If you already run a local postgres, it will create a `changelog` table.
-
-The inital setup or the clean the database call:
-
-```
-yarn migrate:dev
-```
-
-To add new entries, visit `/changelog/_admin` you need to have a Google Account in the Sentry org to login.
-
-#### Seeding
-
-Call
-
-```
-npx prisma db seed
-```