Maintainence: Add lock thread and dependabot

[rubiin]

Lock thread bot would help to clean out stale issues. While dependabot will be great to receive updates

[WikiRik]

In favour of dependabot. It's easier to set up within GitHub than renovate and I think it would provide the same result for this repo.

I'm not so in favour of the lock thread bot. I think people should be able to reply to closed issues/PRs or merged PRs afterwards, especially if the issue has been closed with the original submitter but is still present. If the discussion there becomes too much, maintainers can lock it manually.

[WikiRik]

We might want to include something to close stale issues, for example if they have been inactive for more than a month (especially with the renewed energy in this repo). But I think a reminder and then closing is enough (using actions/stale) and we do not need to lock threads

[rubiin]

Cool. Lets go with the dependabot so we dont run into bigger updates when doing manually

[profnandaa]

Since the lib doesn't have any dependancies but only dev dependencies, I don't think we need deependabot. However, we really need an automation for helping with stale PRs and issues. Suggestions welcome.