Add XCM Payment API methods

[themacexpert]

Description

Adds Information on the XCM Payment API Methods. I found that the most relevant place for this seemed to be the Polkadot API page, if you disagree, lmk and we can relocate.

Checklist

• [x] I have added a label to this PR 🏷️
• [x] I have run my changes through Grammarly
• [ ] 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
• [ ] If pages have been moved around, I have run the move-pages.py script to move the pages and update the image paths on the chinese repo
  • [ ] After the script has been run, I have created an additional PR in moonbeam-docs-cn
• [ ] If images have been added, I have run the compress-images.py script to compress the images.
• [ ] If variables (in variables.yml) need to be updated (such as a name change), I have updated the moonbeam-docs-cn repo to use the new variables
• [ ] If this page requires a disclaimer, I have added one

Corresponding PRs

Please link to any corresponding PRs here.

After Translation Requirements

• [ ] Will need to create PR in moonbeam-docs repo to remove images
• [ ] Will need to create PR in moonbeam-docs repo to remove variables
• [ ] Will need to create PR in moonbeam-mkdocs repo to add redirects for Chinese site
• [ ] No additional PRs are required after the translations are done

Items to be Updated

Please list any of the items that will need to be added or deleted after the translations are done here.

[themacexpert]

Closing this in favor of integrating these changes into #1001