Add GitHub integration with agent_prompts and github_components

[julian-risch]

Summary and motivation

Related to deepset-ai/haystack-experimental#250
@sjrl brought up that one way to keep example files from the experimental Agent around is an integration deepset-ai/haystack-experimental#263 (comment)

Detailed design

Move github_components from experimental to a new integration
Move agent_prompts from experimental to a new integration
The idea is to enable users to run the example notebook (or a version with updated imports) after having installed this new integration

Draft PR: #1637

Checklist

If the request is accepted, ensure the following checklist is complete before closing this issue.

### Tasks
- [ ] The code is documented with docstrings and was merged in the `main` branch
- [ ] Docs are published at https://docs.haystack.deepset.ai/
- [ ] There is a Github workflow running the tests for the integration nightly and at every PR
- [x] A new label named like `integration:<your integration name>` has been added to the list of labels for this [repository](https://github.com/deepset-ai/haystack-core-integrations/labels)
- [ ] The [labeler.yml](https://github.com/deepset-ai/haystack-core-integrations/blob/main/.github/labeler.yml) file has been updated
- [ ] The package has been released on PyPI
- [ ] An integration tile has been added to https://github.com/deepset-ai/haystack-integrations
- [ ] The integration has been listed in the [Inventory section](https://github.com/deepset-ai/haystack-core-integrations#inventory) of this repo README
- [ ] There is an example available to demonstrate the feature
- [ ] The feature was announced through social media