v8.2.0 Define flex and template message types

What's Changed

There are several keywords that can be used for the properties of Template Messages and Flex Messages.

Starting from this version, these keywords are provided. In addition to keywords, you can use strings that specify percentages or pixels, so please convert the keywords to strings if necessary. The original definitions are also written in Flex Message layout and line/line-openapi#46.

line-openapi updates

• Update line-openapi digest to 13b314a by @renovate in #633
• Update line-openapi digest to 16f6311 by @renovate in #634
• Codes are generated by openapi by @github-actions in #635

Dependency updates

• Update dependency axios to v1.6.3 by @renovate in #632

Full Changelog: v8.1.0...v8.2.0