Draft: wip: refactor sql references

Current MR refactors SQL reference section in documentation. It still has WIP status, because:

• references are totally broken
• text stile should be fixed

Moreover, I have re-read the documentation and found lot's of errors there. Some of them were fixed, others are still waiting to be done:

1. Crete procedure - need timeout in diagram
2. Create procedure - broken links for proc body (dml)
3. Create procedure - data type ANY - wtf?!
4. Call - no diagram
5. ALTER procedure RENAME - no diagram
6. SELECT DISTINCT - no diagram
7. SELECT - no option in diagram
8. HAVING - no diagram
9. SELECT - links in params (distinct, join, etc)
10. UNION/EXCEPT - no diagram
11. Follow-up - need to add comparison operators to Func & Op section
12. UPDATE/DELETE - add params section
13. EXPLAIN - refactor diagram

As a reference I was inspired by the RisingWave SQL reference.

@rosik @a.tolstoy please, take a look at the structure and give me some feedback.

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• Staging: https://docs.binary.picodata.io/picodata/stable/reference/