configure dependabot to update samples

[robstoll]

Platform (jvm, js, android):
Extension (none, kotlin 1.3, jdk8): none

Non-Code related feature

Is your feature request related to a problem? Please describe.
Yes, the dependencies of the samples projects get out of date if we don't update them.

Describe the solution you'd like
We already use dependabot and it supports monorepos, thus we can configure it accordingly.

Describe alternatives you've considered
We used non-dependent projects first (still the case for mocha and jasmine samples at the time of writing)

TODO

• setup a corresponding config file for dependabot (https://dependabot.com/docs/config-file/) so that it scans also all subfolders of /samples/ next to the root of the project

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[robstoll]

blocked until we decide what to do with robstoll/atrium-roadmap#69

[robstoll]

since renovate does not support sub-projects (yet), we should setup/configure dependabot instead (samples are outdated now, so if the configuration is done correctly, then dependabot should propose to upgrade them to Atrium v0.13.0)

[uzilan]

I'd like to try to help with this one

[uzilan]

Tried setting it up in my fork and as you said @robstoll - it created PRs for updating Atrium to v0.13.0, as can be seen here: https://github.com/uzilan/atrium/pulls