Add json schema and cli lint command

[anbraten]

addresses #275
preparation for #276

Changes

• add json schema file
• add tests to validate sample pipeline files
• add new command lint to cli to test a directory or single file to use correct schema

woodpecker-cli lint ./pipeline/schema/.woodpecker/

Sample output from `woodpecker-cli lint ./pipeline/schema/.woodpecker/`

# test-branches-exclude-include.yml
❌ Config is invalid
In branches: Must validate one and only one schema (oneOf)
In branches: Invalid type. Expected: array, given: object

# test-branches.yml
❌ Config is invalid
In branches: Must validate one and only one schema (oneOf)
In branches: Invalid type. Expected: array, given: object

# test-clone-skip.yml
❌ Config is invalid
In (root): Additional property skip_clone is not allowed

# test-clone.yml
✅ Config is valid

# test-matrix.yml
✅ Config is valid

# test-multi.yml
❌ Config is invalid
In (root): Additional property depends_on is not allowed

# test-plugin.yml
❌ Config is invalid
In (root): pipeline is required

# test-run-on.yml
❌ Config is invalid
In (root): Additional property run_on is not allowed

# test-service.yml
✅ Config is valid

# test-step.yml
❌ Config is invalid
In pipeline.detached: commands is required
In pipeline.volume.volumes: Invalid type. Expected: string, given: array

# test-when.yml
✅ Config is valid

# test-workspace.yml
✅ Config is valid

---

ref: SchemaStore/schemastore#1845

[6543]

@anbraten please resolve conflict

[6543]

./cli/release/linux/amd64/woodpecker-cli lint .woodpecker/
# docs.yml
✅ Config is valid

# helm.yml
✅ Config is valid

# main.yml
❌ Config is invalid
In pipeline.build-cli.commands: Invalid type. Expected: array, given: string

commands is either string array or string

[anbraten]

That's an error in the schema file. I didn't know / saw that a command is allowed to be just a single string instead of an array with a single item. I will adjust the schema.

[6543]

one question are all schema in pipeline/schema/.woodpecker/ valid by purpose?

[anbraten]

one question are all schema in pipeline/schema/.woodpecker/ valid by purpose?

Yes atm I only added valid configs for all possible options as the impossible options are infinitely large. Schemastore seems to have some negative tests for their hosted schemas. I can try to add something similar.