Support persistent configuration

[murphyatwork]

Feature request

Is your feature request related to a problem? Please describe.

Current we can change FE configuration through admin set frontend config set('x'='y'), but it's not persistent. After restarted, the FE would read from the original file again.

Describe the solution you'd like

Support persisting the configuration changes into another file to survive the restart.

Describe alternatives you've considered

Additional context

[crossoverJie]

I'm interested in this, please assign it to me, thanks.

[crossoverJie]

After communicating with @kevincai , some details were adjusted.

Phase One(finished):

1. When saving the configuration, determine if the current node is the leader.
   1.1 true: Persist the configuration and then synchronize it to other nodes.
   1.2 false: Forward the request to the leader node to execute the process in step one.

Phase Two(todo):
To prevent the issue of data inconsistency caused by the follower nodes' inability to persist, the follower nodes proactively synchronize data with the leader node each time they startup.

Flow chart:

[kevincai]

the pull request is reverted in #54076.

Reopen this issue for further discussion.

cc @gengjun-git

[gengjun-git]

Using new files to store changed configurations can be confusing if users don't know about this feature, so we should introduce a more compatible solution. And some external management components of StarRocks also need to be compatible with this, which is not very friendly to them.

@crossoverJie Thank you for your contribution, we will work together to find a better solution.