Add Diff for OpenAPI Extensions

[reuvenharrison]

This PR adds diff support for OpenAPI Extensions.
The Extension diff format conforms with JavaScript Object Notation (JSON) Patch, for example:

endpoints:
    modified:
        ?   method: POST
            path: /example/callback
        :   extensions:
                modified:
                    x-amazon-apigateway-integration:
                        - oldValue: "201"
                          value: "200"
                          op: replace
                          from: ""
                          path: /responses/default/statusCode
                        - oldValue: http://api.example.com/v1/example/callback
                          value: http://api.example.com/v1/example/calllllllllback
                          op: replace
                          from: ""
                          path: /uri

Behavior Change

Prior to this PR oasdiff diff command didn't report changes to OpenAPI Extensions.
After this PR, the diff will include changes to OpenAPI Extensions by default.
Users can revert to the old behavior (ignoring extensions), by setting --exclude-elements=extensions.

This PR also removes the --exclude-elements flag from oasdiff breaking and oasdiff changelog commands since allowing users to exclude elements in these commands may have unexpected effects like, for example, disabling the tests that depend on x-sunset.

[codecov]

Codecov Report

Attention: Patch coverage is 53.47044% with 181 lines in your changes are missing coverage. Please review.

Project coverage is 83.12%. Comparing base (05b7335) to head (1a24a95).

❗ Current head 1a24a95 differs from pull request most recent head b60ac34. Consider uploading reports for the commit b60ac34 to get more accurate results

Files	Patch %	Lines
diff/json_diff.go	52.63%	18 Missing ⚠️
diff/oauth_flows.go	47.05%	12 Missing and 6 partials ⚠️
diff/info_diff.go	59.25%	7 Missing and 4 partials ⚠️
diff/server_diff.go	47.61%	8 Missing and 3 partials ⚠️
diff/diff.go	25.00%	6 Missing and 3 partials ⚠️
diff/link_diff.go	35.71%	6 Missing and 3 partials ⚠️
diff/schema_diff.go	25.00%	6 Missing and 3 partials ⚠️
diff/security_scheme.go	52.63%	6 Missing and 3 partials ⚠️
diff/variable_diff.go	53.33%	5 Missing and 2 partials ⚠️
diff/contact.go	64.70%	4 Missing and 2 partials ⚠️
... and 20 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #515      +/-   ##
==========================================
- Coverage   84.17%   83.12%   -1.05%     
==========================================
  Files         232      234       +2     
  Lines       12973    13181     +208     
==========================================
+ Hits        10920    10957      +37     
- Misses       1670     1790     +120     
- Partials      383      434      +51     

Flag	Coverage Δ
unittests	83.12% <53.47%> (-1.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.