Workaround invalid schema metric name regex pattern

[vduseev]

Summary

Fixes #178

What's done

1. Migrated off deprecated jsonschema RefResolver.
2. Ignore invalid regex pattern during schema validation. Still check everything else.

Testing

Normal extension written with schema 1.291 in mind

dt-cli on  dev [!⇕] is 📦 v1.6.20 via 🐍 v3.10.13 (.venv) 
❯ ./.venv/bin/dt ext validate-schema --instance ~/Projects/Extensions/python-fortigate/extension/extension.yaml --schema-entrypoint schemas/1.295.0/extension.schema.json

dt-cli on  dev [!⇕] is 📦 v1.6.20 via 🐍 v3.10.13 (.venv) took 3s 
❯ ./.venv/bin/dt ext validate-schema --instance ~/Projects/Extensions/python-fortigate/extension/extension.yaml --schema-entrypoint schemas/1.304.0/extension.schema.json

Latest extension written using schema 1.304

dt-cli on  dev [!⇕] is 📦 v1.6.20 via 🐍 v3.10.13 (.venv) 
❯ ./.venv/bin/dt ext validate-schema --instance ~/Projects/Extensions/otel-collector-prometheus-postgres/src/extension/extension.yaml --schema-entrypoint schemas/1.304.0/extension.schema.json

Purposefully introduced a mistake in the extension.yaml to see if validation still works

dt-cli on  dev [!⇕] is 📦 v1.6.20 via 🐍 v3.10.13 (.venv) took 5s 
❯ ./.venv/bin/dt ext validate-schema --instance ~/Projects/Extensions/otel-collector-prometheus-postgres/src/extension/extension.yaml --schema-entrypoint schemas/1.304.0/extension.schema.json
---------- error 0 ----------
line: 0, column: 0
path: 
cause: 'minDynatraceVersion' is a required property
---------- error 1 ----------
line: 0, column: 0
path: 
cause: Additional properties are not allowed ('minDynatraceVersions' was unexpected)
------------------------------
Error: 2 validation errors total, aborting!

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud