chore(ci): enable Renovate

[AlexanderBarabanov]

What does this PR do?

This PR adds renovate.yml and renovate-config-validator.yml workflows and configuration renovate.json5 to run Renovate as a GitHub Action.
Workflow renovate.yml will run daily and open PRs with suggested security and version upgrades (weekly and monthly).
Instead of using a Personal Access Token (PAT) that is tied to a particular user / faceless account this workflow uses private GitHub App with tuned permissions.
renovate-config-validator.yml workflow will validate changes in renovate.json5.
Dependabot configuration is removed.

Expected behavior - https://github.com/AlexanderBarabanov/model_api/pulls

In addition, Zizmor severity-level and confidence-level are set LOW on pre-commit checks, addressed some low Zizmor findings.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?