Support for getting tags on OCI layout

[jonesbusy]

Description

Support for getting tags on OCI layout

Also breaking to return Tags object instead of a list of strings

Testing done

mvn clean install and one automated tests

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 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.33%. Comparing base (d94f4f4) to head (da8cc70).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/main/java/land/oras/OCILayout.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #256   +/-   ##
=========================================
  Coverage     85.33%   85.33%           
- Complexity      480      484    +4     
=========================================
  Files            34       34           
  Lines          1596     1603    +7     
  Branches        179      179           
=========================================
+ Hits           1362     1368    +6     
  Misses          156      156           
- Partials         78       79    +1     

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