Add update checker management command and documentation

[lvb05]

This PR adds a basic update check mechanism for IntelOwl.
It allows to verify whether the running instance is behind the latest published GitHub release.

Included changes

• Added api_app/core/update_checker.py for version fetch + comparison logic
• Added Django management command: check_updates
• Added settings keys (UPDATE_CHECK_URL, version reuse via existing VERSION)
• Updated README with usage + configuration notes

How to use

python manage.py check_updates

The command will:

1. fetch the latest GitHub release tag
2. normalize version strings
3. compare against the locally configured version
4. log whether a new version is available

No version upgrade happens automatically.
Fixes #2876

Notes

• UPDATE_CHECK_URL is now environment configurable
• local version comes from existing VERSION secret setting
• no new dependencies added
• cron / job scheduler usage referenced in docs if periodic checking is desired.

Checklist

• I have read and understood the rules about how to contribute to this project.
• The pull request targets the correct branch.
• This PR is linked to an approved issue (Add update checker #2876).
• A new plugin (analyzer, connector, visualizer, playbook, pivot, or ingestor) was added or modified.
  N/A – this PR does not introduce or modify any plugins.
• No new external libraries were added.
• Linters (Black, Flake8, Isort) report no errors.
• Tests were added or updated.
  N/A – this PR adds a management command and configuration logic only; existing functionality and tests are unaffected.
• Documentation was updated where appropriate (README updated with usage and configuration).
• GUI changes were made.
  N/A – backend-only change.
• I have addressed any CI or linter warnings triggered after submitting the PR.

[fgibertoni]

Hey @lvb05 thanks for your contribution. Can you please compile the checklist in PR template ? It contains many important step to follow before asking for a review.

[lvb05]

Hey @lvb05 thanks for your contribution. Can you please compile the checklist in PR template ? It contains many important step to follow before asking for a review.

I’ve added and completed the PR checklist in the description.
Please let me know if anything needs adjustment. Thanks!