chore: add dependabot configuration #116

Job	Run time
Lint	1m 7s
Tests (ubuntu-latest, chrome)	48s
Floating Dependencies (ubuntu-latest, chrome)	1m 0s
Tests - ember-lts-3.28	1m 23s
Tests - ember-lts-4.4	1m 14s
Tests - ember-lts-4.8	1m 3s
Tests - ember-classic	53s
Tests - ember-release	1m 14s
Tests - ember-beta	50s
Tests - embroider-safe	1m 21s
Tests - embroider-optimized	1m 30s
Tests - ember-canary	1m 8s
	13m 31s

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