Add skills

[jekalmin]

Objective

• Add skills to make progressive disclosure of context possible.

Caveat

• Since skill scripts can contain anything, it may be harmful if misused.
  • Refer "Security considerations when using Skills" section in this page
  • Still thinking about (not supporting scripts vs supporting scripts)

Needs help

• Where should "skills" folder be placed?
  • if placed in <config>/custom_components/extended_openai_conversation/skills, it might be overwritten when updated.
  • I'm thinking of <config>/.extended_openai_conversation/skills, not sure it's right way.