[2.x] Add dependabot.yml

[cwperks]

Description

Adds dependabot.yml to 2.x branch. This PR adds dependabot.yml directly to 2.x branch. With all of the dependabot PRs against main, labels like backport 2.x, backport 1.x and backport 1.3 must be added to the PR in order to trigger backport bot to backport the PR to the respective branches. This process is manual and causes drifts between release branches if the labels are not added to the PR.

I am creating a PR to add dependabot.yml directly in 2.x and 1.x to keep all of the release branches up to date.

The PR against 1.x includes an automatic label of backport 1.3 so that 1.x and 1.3 can stay synchronized.

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Maintenance

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #3217 (eadd4e5) into 2.x (4ee078b) will decrease coverage by 0.04%.
Report is 1 commits behind head on 2.x.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #3217      +/-   ##
============================================
- Coverage     62.20%   62.17%   -0.04%     
+ Complexity     3312     3308       -4     
============================================
  Files           265      265              
  Lines         19508    19508              
  Branches       3329     3329              
============================================
- Hits          12135    12129       -6     
- Misses         5743     5747       +4     
- Partials       1630     1632       +2     

see 4 files with indirect coverage changes