DAG-Bundle : Git connections ignore credentials for public repositories, causing anonymous rate limit issues

Hi everyone,

### Description

I recently came across the problem, that the git-fetch-requests of the dag-bundle hit the rate-limit of the git-server.
I found out that Airflow cannot **take advantage of a higher rate-limit for authorized git-requests** if the repo is public as it never sends the credentials to the server.

But Airflow could support to **force authentication** for a git connection type via a custom http.extraHeader as additional argument to the git command. This would allow authenticated Git operations even for public repositories.

### Use case/motivation

Git does not authenticate when syncing public repositories, even if login and password are set. This is due to Git’s HTTPS behavior: **it always tries anonymous access first** and only sends credentials if the server responds with a 401 Unauthorized.
=> Public repos typically do not issue a 401, so credentials are never used.

This is problematic because GitLab/GitHub apply different rate limits for authenticated vs anonymous requests. As a result, Airflow tasks can hit anonymous rate limits even when valid credentials are provided.

**A known workaround** is to use Git’s http.extraHeader option to force authentication:
```
B64=$(printf 'x:%s' "" | base64)
git -c http.extraHeader="Authorization: Basic $B64" clone https://gitlab.com//.git
```
This ensures that all requests are authenticated from the first request, avoiding anonymous rate limits.

### Related issues

_No response_

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!
- [x] I am still thinking about a possible solution ...

This functionality probably could be added here 🤔
https://github.com/apache/airflow/blob/main/providers/git/src/airflow/providers/git/hooks/git.py
Perhaps by additional extra arguments
- `config-env` : which represents the git argument `--config-env` - https://git-scm.com/docs/git/2.34.0#Documentation/git.txt---config-envnameenvvar
- `env` : which allows to extent the environment in which git gets executed

This would allow to pass the authentication header to git like you would do it in the shell:
```
export MY_HEADER="Authorization: Basic "
git --config-env=http.extraheader=MY_HEADER clone
```
This would be a very general approach which could also be used for other git-features. But of course it is less intuitiv.

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start in providers/git/src/airflow/providers/git/hooks/git.py and review how Git commands receive connection credentials and extra arguments. Reproduce syncing a public repository with credentials, then add coverage showing that forced authentication avoids anonymous rate limits while preserving existing Git connection behavior.

Written by the indexing model from the issue text.