change case-sensitive parameter default value to false

[sdojjy]

now the default value of changefeed case-sensitive parameter is true, which means it will filter tables in the sensitive model

but cdc always get a lowercase db name from tikv, so in some case, some DDL will be discarded by mistake.
for example

case-sensitive=true
[filter]
rules=["DB1.*"]

ddls

USE DB1;
create table t1 (id int primary key);
alter table t1 rename to t2;
alter table t2 rename to t1;

the last ddl alter table t2 rename to t1; will be ignored

[fubinzh]

/type bug
/severity moderate