Make all values in config classes optional

[fthomas]

This changes RepoConfig and the other *Config classes such that all values are optional and there are no default parameter values except Nones. This allows us to get rid of circe-generic-extras' Configuration.default.withDefaults and deriveConfiguredCodec since missing Option values do not cause an error during decoding. So {} can still be decoded into a RepoConfig, and there are a lot of tests in RepoConfigAlgTest that ensure that sparse configurations with a lot of missing values can still be decoded.

Another benefit of this change is that RepoConfig.show can now use deepDropNullValues so that logged RepoConfigs only include stuff which was actually set by a user. For example, before this change, logging a RepoConfig was similar to this:

INFO  Parsed repo config {
   "commits" : {
     "message" : null
   },
   "pullRequests" : {
     "frequency" : null,
     "grouping" : [
     ],
     "includeMatchedLabels" : null,
     "customLabels" : [
     ]
   },
   "scalafmt" : {
     "runAfterUpgrading" : null
   },
   "updates" : {
     "pin" : [
     ],
     "allow" : [
     ],
     "allowPreReleases" : [
     ],
     "ignore" : [
     ],
     "limit" : null,
     "fileExtensions" : null
   },
   "postUpdateHooks" : null,
   "updatePullRequests" : "always",
   "buildRoots" : null,
   "assignees" : [
   ],
   "reviewers" : [
   ],
   "dependencyOverrides" : [
   ]
 }

The same RepoConfig is now logged as:

INFO  Parsed repo config {
   "updatePullRequests" : "always"
 }

Before merging this PR, I'll squash the commits and provide a better commit message, but for potential reviewers, it should be easier to look at each commit individually.

This continues the work started in #3514 of getting rid of circe-generic-extras so that Scala Steward can be built with Scala 3.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 4 lines in your changes missing coverage. Please review.

Project coverage is 89.63%. Comparing base (12bcad7) to head (fc71579).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...ala/org/scalasteward/core/nurture/NurtureAlg.scala	50.00%	2 Missing ⚠️
...lasteward/core/repoconfig/PullRequestsConfig.scala	66.66%	1 Missing ⚠️
...g/scalasteward/core/repoconfig/UpdatesConfig.scala	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3515      +/-   ##
==========================================
- Coverage   89.64%   89.63%   -0.02%     
==========================================
  Files         171      171              
  Lines        3525     3540      +15     
  Branches      315      331      +16     
==========================================
+ Hits         3160     3173      +13     
- Misses        365      367       +2     

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[alejandrohdezma]

question (non-blocking): Do we still need the None here? Is it just for tests?

_{This comment follows the conventionalcomments.org standard}

[fthomas]

Yes, that is just for the tests. RepoConfigAlgTest would be cluttered with Nones for example.

[alejandrohdezma]

Makes total sense. Thanks!

[fthomas]

This change maybe also enables us to remove nonExistingUpdatePattern since we now can differentiate between the default value and an empty list that was set by a user.

[mzuehlke]

This looks like a very systematic change 👍
Do you think converting the fields of the the case classes into private val would be a good idea to prevent accidental accessing them and forgetting the default value ?

[fthomas]

Do you think converting the fields of the the case classes into private val would be a good idea to prevent accidental accessing them and forgetting the default value ?

Sounds like a good idea to me. I've done that in fc71579.