maint: try using dependabot groups (#147)

## Which problem is this PR solving?

- updates honeycombio/telemetry-team#487

## Short description of the changes

groups are in beta and allow configuring dependabot to open a single pr
for grouped dependencies

trying grouping testing dependencies together, so that a passing test
suite is enough to merge that group

grouping otel together, because more often than not we need to update
all otel versions

## How to verify that this has the expected result

dependabot continues to run and we get fewer PRs

Author: vreynolds

.github/dependabot.yml

@@ -15,4 +15,14 @@ updates:
       - "honeycombio/telemetry-team"
     commit-message:
       prefix: "maint"
-      include: "scope"
+      include: "scope"
+    groups:
+      testing-dependencies:
+        patterns:
+          - "coverage"
+          - "pytest"
+          - "importlib-metadata"
+          - "requests-mock"
+      otel:
+        patterns:
+          - "opentelemetry*"