Metadata: add warning on metadata URI/JSON when compiling storage

Motivation and Context

Related Issue: #1788 (closed).

Description

This MR adds warnings checking the following:

• Checks that %metadata has a key "".
• That the value corresponding to the key "" above is a sha256, http, https, ipfs or tezos-storage URI.
• In case the above is a tezos-storage without host, then the key pointed by the path also exists in %metadata.
• The value corresponding to the key above is valid JSON.

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

Checklist:

• If a new syntax has been introduced, put a message on slack ligo-lsp
• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).