能否在配置文件中增加一个lcn控制开关

## Why you need it?
Is your feature request related to a problem? Please describe in details
我们有些项目，根据客户的场景需求，在部署的时候才能决定是否开启分布式事务（比如如果用不到lcn，就不用部署tm等）。因为是在部署阶段决定，所以通过修改代码@EnableDistributedTransaction的方式不太合适。
能否设置一个开关来控制lcn的启动与否，比如通过配置文件里面的某个参数来控制。

## How it could be?
A clear and concise description of what you want to happen. You can explain more about input of the feature, and output of it.
设置一个开关来控制lcn的启动与否，并且不用改代码的前提下，比如通过配置文件里面的某个参数来控制。

## Other related information
Add any other context or screenshots about the feature request here.

Start by locating the handling for @EnableDistributedTransaction and the configuration-loading entry point. Trace how startup currently enables LCN, then define a configuration property that controls that behavior without code changes. Done means deployment configuration can enable or disable LCN consistently, with tests covering both settings.

Vom Indexierungsmodell aus dem Issue-Text verfasst.