Add github workflow for refreshing cache for the Docsite

[codingone21]

• triggered by any .md / .mdx file changes
• calls onflow/flow/.github/workflows/refresh-doc.yml@master

Issue: https://github.com/onflow/next-docs-v1/issues/201

[codingone21]

Closing this ticket, as we are using kitty-items from /flow repository: https://github.com/onflow/flow/tree/master/docs/content/kitty-items