Enable validating config yaml before run (experimental)

[Kesin11]

fix: #635

Previously, we provided a JSON schema (#675), but it is not used at runtime.
This pull-request enables validation of the config at runtime. Since this feature is still experimental, and for backward compatibility, it won't throw an error, but will show a warning in the console log.

[github-actions]

Code Metrics Report

	master (5f7eafa)	validate_yaml (0ca18ff)	+/-
Coverage	42.2%	43.0%	+0.9%
Test Execution Time	8s	8s	0s

Details

  |                     | master (5f7eafa) | validate_yaml (0ca18ff) |  +/-  |
  |---------------------|------------------|-------------------------|-------|
+ | Coverage            |            42.2% |                   43.0% | +0.9% |
  |   Files             |               28 |                      29 |    +1 |
  |   Lines             |              967 |                     985 |   +18 |
+ |   Covered           |              408 |                     424 |   +16 |
  | Test Execution Time |               8s |                      8s |    0s |

Code coverage of files in pull request scope (43.3% → 44.5%)

Files	Coverage	+/-
src/client/circleci_client.ts	27.4%	0.0%
src/client/circleci_client_v2.ts	13.3%	0.0%
src/client/github_client.ts	31.6%	0.0%
src/client/jenkins_client.ts	27.0%	0.0%
src/config/bitrise_config.ts	100.0%	0.0%
src/config/circleci_config.ts	100.0%	0.0%
src/config/config.ts	73.1%	+6.4%
src/config/github_config.ts	100.0%	0.0%
src/config/jenkins_config.ts	100.0%	0.0%
src/config/schema.ts	100.0%	+100.0%
src/exporter/bigquery_exporter.ts	95.1%	0.0%
src/exporter/exporter.ts	14.3%	0.0%
src/exporter/local_exporter.ts	87.5%	0.0%
src/last_run_store.ts	56.7%	0.0%
src/runner/circleci_runner_v1.ts	34.2%	0.0%
src/runner/circleci_runner_v2.ts	39.1%	0.0%

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Reported by octocov