Add dependabot config

[observingClouds]

Describe your changes

Enables dependabot to keep neural-lams dependencies (pre-commit hooks, GitHub Actions and uv.lock) up-to-date. PRs for each dependency group will be opened on a regular basis.

This is particularly helpful during development to always have the latest dependencies available. One point of discussion is probably how often these checks should be made as there can be many PRs if checked too frequently.

No dependencies need to be changed, but dependabot needs to be setup via the repo settings.

Issue Link

closes #717

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation (Addition or improvements to documentation)

Checklist before requesting a review

• My branch is up-to-date with the target branch - if not update your fork with the changes from the target branch (use pull with --rebase option if possible).
• I have performed a self-review of my code
• For any new/modified functions/classes I have added docstrings that clearly describe its purpose, expected inputs and returned values
• I have placed in-line comments to clarify the intent of any hard-to-understand passages of my code
• I have updated the README to cover introduced code changes
• I have added tests that prove my fix is effective or that my feature works
• I have given the PR a name that clearly describes the change, written in imperative form (context).
• I have requested a reviewer and an assignee (assignee is responsible for merging). This applies only if you have write access to the repo, otherwise feel free to tag a maintainer to add a reviewer and assignee.

Checklist for reviewers

Each PR comes with its own improvements and flaws. The reviewer should check the following:

• the code is readable
• the code is well tested
• the code is documented (including return types and parameters)
• the code is easy to maintain

Author checklist after completed review

• I have added a line to the CHANGELOG describing this change, in a section
  reflecting type of change (add section where missing):
  • added: when you have added new functionality
  • changed: when default behaviour of the code has been changed
  • fixes: when your contribution fixes a bug
  • maintenance: when your contribution is relates to repo maintenance, e.g. CI/CD or documentation

Checklist for assignee

• PR is up to date with the base branch
• the tests pass
• (if the PR is not just maintenance/bugfix) the PR is assigned to the next milestone. If it is not, propose it for a future milestone.
• author has added an entry to the changelog (and designated the change as added, changed, fixed or maintenance)
• Once the PR is ready to be merged, squash commits and merge the PR.

[Copilot]

Pull request overview

Add Dependabot configuration so dependency updates for GitHub Actions, uv.lock, and pre-commit hooks are proposed automatically, and add an automation workflow intended to append changelog entries on Dependabot PRs.

Changes:

• Add .github/dependabot.yml to schedule grouped Dependabot updates for GitHub Actions, uv, and pre-commit.
• Add a GitHub Actions workflow to write a CHANGELOG.md entry when Dependabot opens/updates a PR.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/dependabot.yml	Defines scheduled Dependabot update rules and grouping for key dependency sources.
.github/workflows/dependabot-auto-changelog.yml	Adds automation intended to update the changelog for Dependabot-authored PRs.

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