Support Plugin Settings Backwards Compatibility

[chloe-zh]

Signed-off-by: Chloe Zhang chloezh1102@gmail.com

Description

Comparison between legacy and new settings

Component	Setting Description	Setting Name	Endpoint	Legacy Setting Name	Legacy Endpoint
SQL	Enable/Disable SQL component	plugins.sql.enabled	_plugins/_query/settings or _cluster/settings	opendistro.sql.enabled	_opendistro/_sql/settings
SQL	Config SQL time limit for slow query	plugins.sql.slow_log	_plugins/_query/settings or _cluster/settings	opendistro.sql.slowlog	_opendistro/_sql/settings
SQL	Config the cursor lifetime	plugins.sql.cursor.keep_alive	_plugins/_query/settings or _cluster/settings	opendistro.sql.cursor.keep_alive	_opendistro/_sql/settings
SQL	Enable/Disable SQL delete statement	plugins.sql.delete.enabled	_plugins/_query/settings or _cluster/settings	N/A	N/A
PPL	Enable/Disable PPL component	plugins.ppl.enabled	_plugins/_query/settings or _cluster/settings	opendistro.ppl.enabled	_opendistro/_ppl/settings
Common	Config the memory limit for the circuit breaker	plugins.query.memory_limit	_plugins/_query/settings or _cluster/setting	opendistro.ppl.query.memory_limit	_cluster/settings
Common	Config the query size limit	plugins.query.size_limit	_plugins/_query/settings or _cluster/settings	opendistro.query.size_limit	_cluster/settings

Issues Resolved

#63
#36
opendistro-for-elasticsearch/sql#981

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

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[penghuo]

change the name.

[penghuo]

Thanks for the change!

[dai-chen]

Thanks for the changes!