check new required props for default value

[reuvenharrison]

Added two new checks, for required request properties that have a default value:

• request-property-became-required-with-default
• new-required-request-property-with-default

See also https://github.com/Tufin/oasdiff/issues/555

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.04%. Comparing base (4e41d1d) to head (db1cfcb).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #551 +/- ## ========================================== + Coverage 83.85% 84.04% +0.19% ========================================== Files 227 227 Lines 13016 13012 -4 ========================================== + Hits 10914 10936 +22 + Misses 1687 1666 -21 + Partials 415 410 -5 ``` | [Flag](https://app.codecov.io/gh/Tufin/oasdiff/pull/551/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tufin) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Tufin/oasdiff/pull/551/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tufin) | `84.04% <100.00%> (+0.19%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tufin#carryforward-flags-in-the-pull-request-comment) to find out more.

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