feat: Add goat monster for use in OSB for herblore training

[MikuLittle]

Description:

• The goat monster is useful for OSB as it is one of the most reliable sources of desert goat horns, and the most accessible.
  I opened an issue on OSB here about this: https://github.com/oldschoolgg/oldschoolbot/issues/3000

Changes:

• Added goat.ts to /low/g-m

• Updated the appropriate monster index files

• Ran yarn prepmon to update monsters_data.json

• [X] I have tested all my changes thoroughly.