Add docs for load

[sundy-li]

I hereby agree to the terms of the CLA available at: https://databend.rs/policies/cla/

Summary

Summary about this PR

Changelog

• Documentation

Related Issues

Fixes #3181

Test Plan

Unit Tests

Stateless Tests

[databend-bot]

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[databend-bot]

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[BohuTANG]

/lgtm

[ZhiHanZ]

Do we plan to support cloud provider parameters such as add credentials to copy from external S3 storage?
https://docs.snowflake.com/en/sql-reference/sql/copy-into-table.html#additional-cloud-provider-parameters

[codecov-commenter]

Codecov Report

Merging #3183 (b6383d8) into main (37aa878) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff          @@
##            main   #3183   +/-   ##
=====================================
  Coverage     66%     66%           
=====================================
  Files        673     673           
  Lines      35671   35671           
=====================================
+ Hits       23849   23856    +7     
+ Misses     11822   11815    -7     

Impacted Files	Coverage Δ
query/src/sql/sql_parser_test.rs	79% <100%> (ø)
metasrv/src/meta_service/meta_service_impl.rs	76% <0%> (-1%)	⬇️
query/src/clusters/cluster.rs	53% <0%> (-1%)	⬇️
common/management/src/cluster/cluster_mgr.rs	81% <0%> (+1%)	⬆️
metasrv/src/store/meta_raft_store.rs	78% <0%> (+2%)	⬆️

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[databend-bot]

Wait for another reviewer approval

[BohuTANG]

Do we plan to support cloud provider parameters such as add credentials to copy from external S3 storage? https://docs.snowflake.com/en/sql-reference/sql/copy-into-table.html#additional-cloud-provider-parameters

Sure, more tasks going on it, like:
#2976