Define a subscription storage interface

[pingww]

In order to realize the subscription storage capability in the session storage of the MQTT protocol, We define a subscription storage interface.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 24 lines in your changes missing coverage. Please review.

Project coverage is 31.13%. Comparing base (344cb70) to head (0c16e03).
Report is 278 commits behind head on main.

Files with missing lines	Patch %	Lines
...rocketmq/mqtt/cs/session/loop/SessionLoopImpl.java	50.00%	8 Missing and 3 partials ⚠️
.../apache/rocketmq/mqtt/common/util/SpringUtils.java	0.00%	6 Missing ⚠️
...mqtt/ds/upstream/processor/SubscribeProcessor.java	70.00%	1 Missing and 2 partials ⚠️
...tt/ds/upstream/processor/UnSubscribeProcessor.java	66.66%	1 Missing and 2 partials ⚠️
...a/org/apache/rocketmq/mqtt/cs/starter/Startup.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   30.35%   31.13%   +0.77%     
==========================================
  Files          97       98       +1     
  Lines        4191     4237      +46     
  Branches      661      671      +10     
==========================================
+ Hits         1272     1319      +47     
+ Misses       2676     2666      -10     
- Partials      243      252       +9     

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