Updated dependabot config making updates-entries unique as required by dependabot

[JonasKunz]

Currently dependabot complains about our config:

The property '#/updates/1' is a duplicate. Update configs must have a unique combination of 'package-ecosystem', 'directory', and 'target-branch'

With this PR I attempt to trick dependabot into still evaluating both of our updates-rules at least on the apm-agent-plugins submodules, from which to my understanding the monthly-exemptions originate.

If the maven dependabot strategy is implemented as described here, it should hopefully work. Unfortunately I wasn't able to find any actual documentation on the behaviour with overlapping directories.

We will see whether after this PR dependabot still continues opening PRs weekly for the apm-agent-plugins or not.

[apmmachine]

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• Start Time: 2022-10-04T17:39:14.396+0000

• Duration: 60 min 15 sec

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Passed	3156
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Total	3192

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