Missing const typing support

[adamaltman]

Describe the bug

Are we missing const from here: https://github.com/Redocly/redocly-cli/blob/main/packages/core/src/typings/openapi.ts

• https://json-schema.org/understanding-json-schema/reference/const

To Reproduce n/a

Expected behavior

To be able to use the type tree to traverse the values including enum (is already in the typings) and const (missing) values.

Logs

n/a

OpenAPI description

3.1

Redocly Version(s)

latest

Node.js Version(s)

n/a

Additional context

Relates to writing some advanced plugins/extensions.