feat: query to get all schema of the space

[wey-gu]

This is needed in some cases i.e. support nebulagraph query in Langchain.

From the application layer, sometimes we could leverage meta-client to do so but it's not applicable for all cases.

Possible options:

• introduce a query to show all schemas in one go
• support variable/pipeline on desc query like:

(root@nebula) [basketballplayer]> show edges AS e| desc edge $-.e
[ERROR (-1004)]: SyntaxError: syntax error near `AS'

Wed, 31 May 2023 15:27:30 CST