tracking: sql variable features

[sundy-li]

Summary

• [x] basic SQL variable support in session level #16134
• [x] IDENTIFIER function support SQL variable IDENTIFIER($my_table_name), replace ident in NameResolutionContext #16264
• [x] support serde/deserde variables to HTTP response and apply variables changes during session start (work like settings)
• [x] #16274
• [x] drivers support SQL variables (databend-go, bendsql, databend-jdbc)
• [ ] docs

[TCeason]

Got it

[TCeason]

Add config or setting about variable quota.

Personally, I'm more biased towards setting.

Now we has user role quota config. But user and role is a global tenant level object. But var just a session level object.

[sundy-li]

Add config or setting about variable quota.

Personally, I'm more biased towards setting.

Now we has user role quota config. But user and role is a global tenant level object. But var just a session level object.

No need now.

[sundy-li]

cc @soyeric128 Let's add documents about sql variables.