Add `information_schema` database for all catalog.
This is useful when using BI tools to connect to Doris,
the tools can get meta info from `information_schema`.
This PR mainly changes:
1. There will be a `information_schema` db in each catalog.
2. Each `information_schema` db only store the meta info of the catalog it belongs to.
3. For `information_schema`, the `TABLE_SCHEMA` column's value is the database name.
4. There is a new global variable `show_full_dbname_in_info_schema_db`, default is false, if set to true,
The `TABLE_SCHEMA` column's value is the like `ctl.db`, because:
When connect to Doris, the `database` info in connection url will be: `xxx?db=ctl.db`.
And then some BI will try to query `information_schema` with sql like:
`select * from information_schema.columns where TABLE_SCHEMA = "ctl.db"`
So it has to be format as `ctl.db`
eg, the `information_schema.columns` table in external catalog `doris` is like:
```
mysql> select * from information_schema.columns limit 1\G
*************************** 1. row ***************************
TABLE_CATALOG: doris
TABLE_SCHEMA: doris.__internal_schema
TABLE_NAME: column_statistics
COLUMN_NAME: id
ORDINAL_POSITION: 1
COLUMN_DEFAULT: NULL
IS_NULLABLE: NO
DATA_TYPE: varchar
CHARACTER_MAXIMUM_LENGTH: 4096
CHARACTER_OCTET_LENGTH: 16384
NUMERIC_PRECISION: NULL
NUMERIC_SCALE: NULL
DATETIME_PRECISION: NULL
CHARACTER_SET_NAME: NULL
COLLATION_NAME: NULL
COLUMN_TYPE: varchar(4096)
COLUMN_KEY:
EXTRA:
PRIVILEGES:
COLUMN_COMMENT:
COLUMN_SIZE: 4096
DECIMAL_DIGITS: NULL
GENERATION_EXPRESSION: NULL
SRS_ID: NULL
```
6. Modify the behavior of
- show tables
- shwo databases
- show columns
- show table status
The above statements may query the `information_schema` db if there is `where` predicate after them
ebfbe0c8dd