enh: corrent slimit/limit statement

enh(query): improve mode function page buffer allocation

feat: add sql command 'balance vgroup leader'

merge 3.0

* docs: add taoskeeper start as service

* docs: update taoskeer launch

feat: add sql command 'balance vgroup leader'

fix: create function error for json/decimal/blob/varbinary type

docs: release 3.0.3.1

feat: alter database wal_retention_period/wal_retention_size

* docs: this line is inaccurate, in current connector-python repo, it require python >= 3.6.2 because there is a dependence iso8601

* docs: append websocket doc for python connector

* docs: fix tabitem

---------
Co-authored-by: NAdam Ji <jrgwyz@163.com>

* docs: this line is inaccurate, in current connector-python repo, it require python >= 3.6.2 because there is a dependence iso8601

* docs: append websocket doc for python connector

---------
Co-authored-by: NAdam Ji <jrgwyz@163.com>

* feat(driver): add schemaless raw insert for jdbc

* feat: add jni reqId

* fix: change API

* fix: change method name

* fix: error code to hex format

enhance: add udf context from plugin traceability

fix:add tips for tmq consume

fix:add tips for tmq consume

docs: refine tmq configuration

docs: refien tmq configuration

docs: add flush database doc