optimizes the structure of config module and discovery module

[xingfudeshi]

Ⅰ. Describe what this PR did

In practical applications, for configuration centers and registries, multiple types are not used at the same time, such as Zookeeper, Nacos and so on. Therefore, these dependencies should be optional, allowing users to decide what dependencies to download.
So,this PR provides a way for users to decide which dependencies to use and download by themselves. By default, File-based configuration and registry have been provided.
for example:
if you need only the support for Spring,you can import the following dependency

Maven dependency

<fescar.version>0.4.2</fescar.version>

<dependency>
    <groupId>com.alibaba.fescar</groupId>
    <artifactId>fescar-spring</artifactId>
    <version>${fescar.version}</version>
</dependency>

As described before,by default,only File-based configuration and registry will be provided.so,in registry.conf,the value of type for both registry and config should be file.

registry {
  # file 、nacos 、eureka、redis、zk、consul
  type = "file"
...
config {
  # file、nacos 、apollo、zk
  type = "file"
...

In another case,you may want to use the Nacos as the configuration center,and the consul for registry,then you just need import two more dependencies as bellow:

<dependency>
    <groupId>com.alibaba.fescar</groupId>
    <artifactId>fescar-config-nacos</artifactId>
    <version>${fescar.version}</version>
</dependency>
<dependency>
    <groupId>com.alibaba.fescar</groupId>
    <artifactId>fescar-discovery-consul</artifactId>
    <version>${fescar.version}</version>
</dependency>

and modify the value in registry.conf,the final configuration should look like the following:

registry {
  # file 、nacos 、eureka、redis、zk、consul
  type = "consul"
...
config {
  # file、nacos 、apollo、zk
  type = "nacos"
...

In addition, you can use the following two dependencies, which import all Seata-supported configuration centers and registries.

<dependency>
    <groupId>com.alibaba.fescar</groupId>
    <artifactId>fescar-config-all</artifactId>
    <version>${fescar.version}</version>
</dependency>
<dependency>
    <groupId>com.alibaba.fescar</groupId>
    <artifactId>fescar-discovery-all</artifactId>
    <version>${fescar.version}</version>
</dependency>

Ⅱ. Does this pull request fix one issue?

#760
#755
#601

Ⅲ. Why don't you add test cases (unit test/integration test)?

i have done the integration testing.and,i didn't modify the original implementation.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #774 into develop will increase coverage by 1.66%.
The diff coverage is 18.75%.

@@             Coverage Diff              @@
##             develop    #774      +/-   ##
============================================
+ Coverage      32.73%   34.4%   +1.66%     
+ Complexity       936     889      -47     
============================================
  Files            228     215      -13     
  Lines           9103    8299     -804     
  Branches        1108     996     -112     
============================================
- Hits            2980    2855     -125     
+ Misses          5766    5104     -662     
+ Partials         357     340      -17

Impacted Files	Coverage Δ	Complexity Δ
...ar/discovery/registry/FileRegistryServiceImpl.java	61.53% <ø> (ø)	7 <0> (?)
...libaba/fescar/discovery/registry/RegistryType.java	40% <ø> (ø)	2 <0> (?)
...r/discovery/loadbalance/RoundRobinLoadBalance.java	66.66% <ø> (ø)	3 <0> (?)
...scar/discovery/loadbalance/LoadBalanceFactory.java	66.66% <ø> (ø)	1 <0> (?)
...car/discovery/loadbalance/AbstractLoadBalance.java	66.66% <ø> (ø)	3 <0> (?)
...escar/discovery/loadbalance/RandomLoadBalance.java	100% <ø> (ø)	2 <0> (?)
...ery/registry/consul/ConsulRegistryServiceImpl.java	0% <ø> (ø)	0 <0> (?)
...covery/registry/consul/ConsulRegistryProvider.java	0% <0%> (ø)	0 <0> (?)
...scar/core/rpc/netty/AbstractRpcRemotingClient.java	20.57% <5%> (+2.66%)	7 <0> (ø)	⬇️
...aba/fescar/discovery/registry/RegistryFactory.java	50% <50%> (ø)	2 <2> (?)
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 117f3da...78f9ae4. Read the comment docs.

[slievrly]

LGTM

[lovepoem]

LGTM