Merge `new project` templates into one (#24985)

Merge `new project` templates into one (#24985)

Additionally simplify the `new project` template slightly.

Review hint: Disable whitespace changes.

<details><summary>Before</summary>

## New repo project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/4de977e8-3688-45cd-8832-49b001e6f249)

## Edit repo project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/daaf353f-6c99-48bd-b37a-a3bc64459079)

## New user/org project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/6a5a3be5-f51a-4599-b75c-7adb9710d2fa)

## Edit user/org project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/a4768f49-cf46-4773-8a0f-54dfdcc1c1b8)
</details>

<details><summary>After</summary>

## New repo project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/3d0ac8a0-850a-4743-963c-71c66ef38d07)

## Edit repo project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/6b86a1cd-e360-4a9b-aaf7-af032d0d991a)

## New user/org project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/a7b0964c-e4c7-4924-842a-52a58499bc36)

## Edit user/org project

![grafik](https://github.com/go-gitea/gitea/assets/51889757/0fbc5605-afee-49bd-a44a-8646f8c55681)
</details>

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Co-authored-by: Giteabot <teabot@gitea.io>