OpenAPI: use yaml linter

[kevinjqliu]

This PR adds a yaml linter for rest-catalog-open-api.yaml and ../aws/src/main/resources/s3-signer-open-api.yaml to keep formatting consistent, using yamllint to check for formatting issues.

Introduced a few new Makefile commands

make validate-spec
make lint-spec
make lint # runs both above

The linter rules are kept in open-api/.yamllint

[Fokko]

This looks great @kevinjqliu, one comment around the line length

[Fokko]

This seems pretty long?

[kevinjqliu]

yea, agreed. im deferring the line-length lint fix for later. want to get the linter installed asap

[geruh]

Nice LGTM! a yaml linter that plays well with the headers

[kevinjqliu]

All changes to aws/src/main/resources/s3-signer-open-api.yaml and open-api/rest-catalog-open-api.yaml are formatting / cosmetic only.
I tried to address each class of change in individual commits, https://github.com/apache/iceberg/pull/14686/commits

Specifically, here are the list of yamllint errors:
Fixed

• too few spaces before comment: expected 2 (comments)
• too few spaces after comma (commas)
• trailing spaces (trailing-spaces)
• wrong indentation: expected 16 but found 18 (indentation)
• too many blank lines (3 > 2) (empty-lines)

Ignored

• too many spaces inside braces (braces)
• too many spaces inside brackets (brackets)
• too many spaces inside empty braces (braces)
• too many spaces inside empty brackets (brackets)
• line too long (123 > 120 characters) (line-length)

[kevinjqliu]

sent out an email to dev@. if there are no objections by EOW, i'll merge this PR

https://lists.apache.org/thread/g4yqzltzs2n4jsdpln66yzz439vy0bpy

[kevinjqliu]

thanks for the review everyone!