Add support for docker content types

[jonesbusy]

Description

Would fix: #194

Testing done

CI and some OCI layout export from a legacy docker layout

Submitter checklist

• I have read and understood the CONTRIBUTING guide
• I have run mvn license:update-file-header, mvn spotless:apply, pre-commit run -a, mvn clean install before opening the PR

[codecov]

Codecov Report

Attention: Patch coverage is 89.18919% with 4 lines in your changes missing coverage. Please review.

Project coverage is 84.91%. Comparing base (1acec5c) to head (9037ba2).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/main/java/land/oras/Registry.java	88.57%	0 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #195      +/-   ##
============================================
- Coverage     85.06%   84.91%   -0.15%     
- Complexity      367      375       +8     
============================================
  Files            29       29              
  Lines          1272     1286      +14     
  Branches        132      137       +5     
============================================
+ Hits           1082     1092      +10     
  Misses          131      131              
- Partials         59       63       +4     

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