chore: support auto bump container images with dependabot.

[liangyuanpeng]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

support auto bump container images with dependabot, but I'm not sure whether we should treat release branch like this, it's means we need to update release branch from this file when a new release is out.

option2 is only auto bump container image for master and cherry pick the PR of dependabot to release branch if need.

Which issue(s) this PR fixes:
Fixes #4908

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.34%. Comparing base (3fc8ef5) to head (26db029).
Report is 70 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4932      +/-   ##
==========================================
+ Coverage   53.14%   53.34%   +0.19%     
==========================================
  Files         251      252       +1     
  Lines       20415    20482      +67     
==========================================
+ Hits        10850    10926      +76     
+ Misses       8852     8835      -17     
- Partials      713      721       +8     

Flag	Coverage Δ
unittests	53.34% <ø> (+0.19%)	⬆️

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[RainbowMango]

Amazing!

I'm not sure whether we should treat release branch like this, it's means we need to update release branch from this file when a new release is out.

I think letting Dependabot handle these things for both master and release branches would be better.

Two more things we should consider about:

1. we need to update the configuration(.github/dependabot.yml) after a new release and remove the one that is out of maintenance.
2. The PR sent by Dependabot doesn't use the PR template, how to set the release notes?

[liangyuanpeng]

1. We can update it when needed together with

   karmada/.github/workflows/ci-schedule-compatibility.yaml

   Line 20 in c7ca958

   karmada-version: [ release-1.7, release-1.8, release-1.9 ]

   , so it won't be forgotten

2. apparently I forgot about this, dependabot can't cover this. We may need other things to do this. like: edit the PR description if PR author is dependabot[bot] and PR have the label docker
   2.1) write the javascript with github action actions/github-script
   2.2) wirte the code in karmada with go repo and run it with github action.
   2.3) write a prow plugin.

For simplicity I would choose option 2.2, other idea is welcome .

[RainbowMango]

We can update it when needed together with

OK.

apparently I forgot about this, dependabot can't cover this. We may need other things to do this. like: edit the PR description if PR author is dependabot[bot] and PR have the label docker
2.1) write the javascript with github action actions/github-script
2.2) wirte the code in karmada with go repo and run it with github action.
2.3) write a prow plugin.

For simplicity I would choose option 2.2, other idea is welcome .

Will see, those solutions sound a little bit heavy.

[RainbowMango]

/assign

[RainbowMango]

/lgtm
/approve

[karmada-bot]

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