Add flip for fungible tokens metadata

[alilloig]

Closes: https://github.com/onflow/flow-ft/issues/81

Description

Flip for creating a Metadata standard for fungible tokens.

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For contributor use:

• [x] Targeted PR against master branch
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• [x] Updated relevant documentation
• [x] Re-reviewed Files changed in the Github PR explorer
• [x] Added appropriate labels

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Name	Status	Preview	Updated
flow-docs	✅ Ready (Inspect)	Visit Preview	Aug 16, 2022 at 8:51PM (UTC)

[alilloig]

I could really use some help with the Motivation and User Benefit writing!

[alilloig]

I'm still missing any related issues, and will much appreciate a look at Objective, Motivation & User Benefit, haven't feel specially litterateur with those

[alilloig]

@pgebheim should I merge the FLIP here or we should only take it to the FLIPs repo???

[pgebheim]

Let's merge here and I'll port to the FLIPs repo