Add a meaningful PR body for parent/child commands

[justinharringa]

This will add a body like the following to parent and child commands instead of f9ed6ea5-6e74-4338-a629-50c5c6807a6b:

alpine changed recently. This pull request ensures you're using the latest version of the image and changes alpine to the latest tag: 42

New value: alpine:42

After this, we just need to do this for the all subcommand in order for it to also handle #149

[codecov]

Codecov Report

Merging #152 into master will increase coverage by 0.59%.
The diff coverage is 96.29%.

@@             Coverage Diff              @@
##             master     #152      +/-   ##
============================================
+ Coverage     72.81%   73.40%   +0.59%     
- Complexity      212      217       +5     
============================================
  Files            15       16       +1     
  Lines           765      786      +21     
  Branches        106      107       +1     
============================================
+ Hits            557      577      +20     
  Misses          187      187              
- Partials         21       22       +1     

Impacted Files	Coverage Δ	Complexity Δ
...e/dockerfileimageupdate/model/PullRequestInfo.java	90.90% <90.90%> (ø)	6.00 <6.00> (?)
...ce/dockerfileimageupdate/subcommands/impl/All.java	58.53% <100.00%> (+0.68%)	16.00 <0.00> (ø)
.../dockerfileimageupdate/subcommands/impl/Child.java	100.00% <100.00%> (ø)	4.00 <0.00> (ø)
...dockerfileimageupdate/subcommands/impl/Parent.java	53.33% <100.00%> (+3.33%)	8.00 <0.00> (ø)
...kerfileimageupdate/utils/DockerfileGitHubUtil.java	86.20% <100.00%> (-0.12%)	41.00 <3.00> (-1.00)

[justinharringa]

@afalko do you mind poking this one again? The update from master invalidated your review.