feat: resolve refs in config

[tatomyr]

What/Why/How?

This allows using $ref in config files like this:

# redocly.yaml
seo:
  $ref: seo.yaml
rbac: 
  $ref: rbac.yaml

⚠️ When using the push command with $ref's in config file, user should explicitly upload all referenced files in the config using --files option.

• Resolve $refs in config files
• Add basic linting support
• Extend config node types to be linted
• Add basic support for VS Code extension
• Check compatibility with other tools (scout and portal)
• Look into Error resolving $ref pointer redoc#740 (comment) (is not related; better to be handled in a separate MR)

Also fixed a couple of issues with resolving refs and formatting the output.

Reference

Resolves #1219

Testing

Screenshots (optional)

Check yourself

• Code is linted
• Tested with redoc/reference-docs/workflows (internal)
• All new/updated code is covered with tests

Security

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 0231d42

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@redocly/openapi-core	Minor
@redocly/cli	Minor

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

Command	Mean [s]	Min [s]	Max [s]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	1.064 ± 0.029	1.037	1.121	1.00
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	1.070 ± 0.020	1.035	1.102	1.01 ± 0.03

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	76.31%	4100/5373
🟡	Branches	66.29%	2183/3293
🟡	Functions	68.42%	663/969
🟡	Lines	76.51%	3847/5028

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟡	core/src/utils.ts	77.6%	63.64%	77.27%	77.59%
🟢	... / config-resolvers.ts	83.43%	73.36%	100%	84.05%

Test suite run success

653 tests passing in 94 suites.

Report generated by 🧪jest coverage report action from 0231d42

[IgorKarpiuk]

LGTM

[tatomyr]

The link checker started failing for some strange reason (Dockerhub responds with 429 status despite being available from the browser), even on the main branch. I'm not sure what caused that, but it's not related to the changes.
So I'm going ahead and merging this.