Provide Library Metadata

[cari-lynn]

Use cases

• Using the feature to inspect data values schema as OpenAPIv3 schema I want to provide the info metadata such as version and title of the schema. (Currently these are populated with basic default values) Issue: Generate OpenAPI info from annotation #539
• As a ytt library maintainer, I want to provide metadata to consumers of the library. (eg: Package name, version) So they may verify a minimum version is used or include the metadata in the output.
• Add your use case ⬇️

Describe the solution you'd like
I want a way to provide metadata for a library. This could be through an annotation:
#@schema/library-title "spellchecker" or
#@library/metadata {'title': 'spellchecker', 'version': '0.2.0'} or
#@schema/info {'title': 'spellchecker', 'version': '0.2.0'}

or through a flag:
--library-meta title=spellchecker

Anything else you would like to add:
We don't currently have any library metadata features except for the version module.
This could belong in the same file as the minimum required version. These two concepts both belong to the concept of a library.
version.require_at_least("0.26.0")

🤔 A consideration is how this would play with kapp-controller Packages which are often used with ytt, and have a concept of metadata and versions. Is there a way to ensure the same version of a ytt library and a package? Do these two things need distinct metadata?

🤔 What do other languages/programs use to provide metadata? Some things that come to mind are go.mod, helm, java, or goland..

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[pivotaljohn]

Another approach is to capture this library-wide information in a fixed-named configuration file:

.ytt-info

---
name: spell-checker
description: Checks yer spelling
version: 0.0.1
minimum_ytt: 0.38.0
deprecated: false

ytt looks for an loads this file as a part of building a workspace.Library and checks the current version.Version a la:

https://github.com/vmware-tanzu/carvel-ytt/blob/9cc6a8b8bbf979a8980c4764d42b63e544f2a045/pkg/yttlibrary/version.go#L61