Add page on sending ERC-20s via XCM

[eshaben]

Description

This adds a new page to the XC-20s section of the docs on how to send ERC-20s using the X-Tokens Pallet and Precompile. It also moves away from mintable xc-20s, favoring local xc-20s instead.

Still need to figure out the naming situation but for now just referring to regular old ERC-20s as ERC-20s... groundbreaking, I know.

Checklist

• If this requires translations for the moonbeam-docs-cn repo, I have created a ticket for the translations in Jira
• Add redirects

After Translation Requirements

• Add redirects to mkdocs-cn for xc-20.md
• Remove images that are no longer being used (polkadot.js apps)
• Remove index page and banner image for xc-20s page

[albertov19]

Hey because this is still being worked on right now, let's convert this into a draft

[eshaben]

Once other XCM pages are updated to XCM v3, I'll circle back to update the send-erc20s.md file to include these snippets: 'text/xcm/xcm-precompile-multilocation.md' and 'text/xc-20/xtokens/multilocation-structures.md'. Didn't want to go down the rabbit hole of updating these snippets and the pages they are on in this PR

[eshaben]

@albertov19 this can be reviewed. I only updated the new page to reflect changes to XCM v3. I've been making changes to other related pages in another branch, so I'll open another PR for those pages 🙂

[eshaben]

With all the changes I ended up moving the xtokens v3 update into this PR 😅

@albertov19 ready for review again

[albertov19]

LGTM! Let's doo iitttttt!

[albertov19]

@eshaben I've approved the PR, please check my commits just to check everything looks good :)

[eshaben]

This PR can be merged once this one is approved: moonbeam-foundation/moonbeam-docs-cn#276