improve xc20 and xc integration docs

[eshaben]

Description

This PR addresses a few items:

• Create new XC Registration section
• Split XC integration information out to several pages: Forum templates, Asset Registration, Channel Registration
• Remove channel registration info from XC-20s overview page
• Remove interact with XC-20s content from XC-20s overview page and add to new Interact with XC-20s page
• Add notes on local XC-20 limitations: must match the transfer fn selector described in EIP-20 and limitations on gas
• Adds some new diagrams to summarize asset registrations flows

Checklist

• If this requires translations for the moonbeam-docs-cn repo, I have created a ticket for the translations in Jira
• If pages have been moved around, I have created an additional PR in moonbeam-mkdocs to update redirects

Corresponding PRs

Redirects PR: papermoonio/moonbeam-mkdocs#135

After Translation Requirements

• Will need to create PR in moonbeam-docs repo to remove images
• Will need to create PR in moonbeam-mkdocs repo to add redirects for Chinese site

Items to be Updated

👉 Need to apply same redirects for CN site (refer to PR in Corresponding PRs section)
👉 Need to remove the /builders/interoperability/xcm/xc-integration.png index page icon along with all of the images in /builders/interoperability/xcm/xc-integration/*

[albertov19]

Left some minor feedback. Thanks for re-arranging the pages, it is much better now <3

[albertov19]

LGTM!