feat: prefix option for timestamp index and value column (#7125)

* refactor: use GREPTIME_TIMESTAMP const

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* feat: add config for default ts col name

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* refactor: replace GREPTIME_TIMESTAMP with function get

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: update config doc

* fix: test

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: remove opts on flownode and metasrv

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: add validation for ts column name

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: use get_or_init to avoid test error

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: fmt

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: update docs

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: using empty string to disable prefix

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: update comment

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

* chore: address CR issues

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

---------

Signed-off-by: shuiyisong <xixing.sys@gmail.com>

config/standalone.example.toml

@@ -2,6 +2,10 @@
 ## @toml2docs:none-default
 default_timezone = "UTC"
 
+## The default column prefix for auto-created time index and value columns.
+## @toml2docs:none-default
+default_column_prefix = "greptime"
+
 ## Initialize all regions in the background during the startup.
 ## By default, it provides services after all regions have been initialized.
 init_regions_in_background = false