[ISSUE #7109] support the mixed topic type

[dingshuangxi888]

Which Issue(s) This PR Fixes

Fixes #7109

Brief Description

Currently, many users are using a single topic to send messages of different types. However, in the future, there is a desire to exert strict control over message types. Message type validation has already been implemented in the Proxy component. To support the transition of existing users to the Proxy architecture, a new message type called "MIXED" should be introduced to facilitate the migration process.

How Did You Test This Change?

1. create a topic with MIXED message type.
2. send messages with different message type, and verify the result.
3. receive messages in currently and orderly mode, and verify the result.

[drpmma]

LGTM

[codecov-commenter]

Codecov Report

Merging #7110 (496fa3c) into develop (ab61183) will decrease coverage by 0.02%.
The diff coverage is 73.33%.

@@              Coverage Diff              @@
##             develop    #7110      +/-   ##
=============================================
- Coverage      42.74%   42.72%   -0.02%     
  Complexity      9303     9303              
=============================================
  Files           1139     1139              
  Lines          81259    81262       +3     
  Branches       10636    10637       +1     
=============================================
- Hits           34734    34722      -12     
- Misses         42188    42199      +11     
- Partials        4337     4341       +4     

Files Changed	Coverage Δ
...or/validator/DefaultTopicMessageTypeValidator.java	33.33% <0.00%> (-6.67%)	⬇️
...he/rocketmq/proxy/grpc/v2/route/RouteActivity.java	90.00% <88.88%> (-1.13%)	⬇️
...he/rocketmq/common/attribute/TopicMessageType.java	50.00% <100.00%> (+2.17%)	⬆️

... and 24 files with indirect coverage changes

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