Extend dependabot to cover pip, conda, and pre-commit

[antonwolfy]

This PR extends the Dependabot configuration so the pinned dependency versions used across CI are tracked and bumped automatically, and consolidates pre-commit hook updates into Dependabot instead of a dedicated workflow.

Previously only the github-actions ecosystem was covered.

Three new updates entries:

• pip (/environments) — updates the pinned PyPI packages in the environments/*.txt files (base_build_docs.txt, coverage.txt, dpctl_pkg.txt). Dependabot scans the directory for requirements-like files regardless of name and reads any --index-url (e.g. the dppy dev channel in dpctl_pkg.txt) directly from the file.
• conda (/environments) — updates the plain conda-forge pkg=X.Y.Z pins in the env YAML files consumed by setup-miniconda.
• pre-commit (/) — updates hook versions in .pre-commit-config.yaml.

Also PR deletes .github/workflows/pre-commit-autoupdate.yml. Its flow is now handled by the pre-commit Dependabot entry.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/2983/index.html

[coveralls]

Coverage is 78.073% — extend-dependabot-config-to-pip-conda-managers into pin-conda-to-avoid-installing-faulty-build. No base build found for pin-conda-to-avoid-installing-faulty-build.

[github-actions]

Array API standard conformance tests for dpnp=0.21.0dev2=py313h509198e_11 ran successfully.
Passed: 1369
Failed: 4
Skipped: 7