chore: update contributing guide and mark technical package.jsons private

[tatomyr]

What/Why/How?

• Fixed the CONTRIBUTING guide
• Marked technical package.jsons as private for clarity

Reference

Testing

Screenshots (optional)

Check yourself

• Code changed? - Tested with redoc/reference-docs/workflows (internal)
• All new/updated code is covered with tests
• New package installed? - Tested in different environments (browser/node)

Security

• Security impact of change has been considered
• Code follows company security practices and guidelines

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4f354bd

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	992.1 ± 41.8	967.9	1109.2	1.01 ± 0.05
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	984.4 ± 15.4	957.6	1011.8	1.00

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	78.6%	5053/6429
🟡	Branches	67.18%	2059/3065
🟡	Functions	73.16%	834/1140
🟡	Lines	78.88%	4767/6043

Test suite run success

836 tests passing in 120 suites.

Report generated by 🧪jest coverage report action from 4f354bd