docs(generateMetadata): update code blocks to include filename (#67745)
On the generateMetadata page [^1], the code blocks in "robots" [^2] and
"Types" [^3] section do not have the `filename` prop.
According to the Docs Contribution Guide [^4], code blocks should
include the `filename` prop for clarity.
[^1]:
https://nextjs.org/docs/app/api-reference/functions/generate-metadata
[^2]:
https://nextjs.org/docs/app/api-reference/functions/generate-metadata#robots
[^3]:
https://nextjs.org/docs/app/api-reference/functions/generate-metadata#types
[^4]:
https://nextjs.org/docs/community/contribution-guide#language-and-filename
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
Co-authored-by: Jiwon Choi <devjiwonchoi@gmail.com>