Add metadata construction guide to the docs

[YamenMerhi]

do not merge or review (as the code might change in the lsp-utils PR) until @lukso/lsp-utils is released with this PR https://github.com/lukso-network/lsp-utils/pull/58

[github-actions[bot]]

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[Hugoo]

hi @YamenMerhi - the PR you refer to in the description has been merged - is this PR now ready for review and merge?