Export named validations to openApi properties

[peschmae]

This pull requests, exposes the attributes for the named #@schema/validations to the openApi schema, where a direct mapping is possible.

Type	ytt validation	openapi validation
string	min_len	minLength
string	max_len	maxLength
integer	min	minimum
integer	max	maximum
any	one_of	enum

The PR includes tests for all those validations.

Fixes #897

[prembhaskal]

will try to review this week.

[peschmae]

Just saw the linting errors, and will look into them.

Should I squash my commits and force push, or is it fine to have mutliple commits, and the will be squashed when merged?

[prembhaskal]

you can have multiple commits and then squash them before merging.

[peschmae]

Any change to get a review on this?
Compared to #901 this is a smaller change and would allow to integrate the conversion from openapi to json schema, in a separate tool if the other PR wouldn't be merged.

[joaopapereira]

Added some nitpick changes more stylistic than anything.
Generally, the PR looks good.

[peschmae]

Ammended whitespace cleanup into latest commit, and force pushed

[sethiyash]

LGTM!

[joaopapereira]

LGTM