feat(remote_wal): add skeleton for remote wal related to meta srv

[niebayes]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

The remote wal project involves modifying a bunch of codes and I've observed that reviewers are finding it challenging to grasp the overall scope of the remote wal project. This PR is proposed to try to speed up the review process.

Details

• We are designing a WalOptions that stores wal options allocated at the granularity of a region.

• We are designing a WalOptionsAllocator for the granular allocation of wal options based on regions. It internally maintains a KafkaTopicManager for allocating Kafka wal topics if the allocator is of type WalOptionsAllocator::Kafka. For efficiency, this allocator also supports batch allocation of wal options.

• The KafkaTopicManager primarily consists of a topic pool and a topic selector.

  • During the initialization of the topic manager, we first read all already created topics from the kv backend. If there aren't enough topics created, we use the rskafka client to request creating more topics from the Kafka cluster. The names of the created topics are stored in the kv backend to avoid duplicate creation upon restart. These topic names are also cached in the in-memory topic pool.
  • The topic selector is responsible for selecting a topic from the topic pool based on a certain strategy (e.g., default round-robin).

• When the Meta srv starts, we initialize the WalOptionsAllocator. It is then maintained by the TableMetadataAllocator in the DdlManager.

• When handling a create table request, the create interface of the TableMetadataAllocator in the DdlManager is called. At this point, we invoke the WalOptionsAllocator to allocate wal options for each region of the table. The allocated wal options are passed to the procedure manager and used during the execution of the create table operation.

• We modify DatanodeTableValue to include a wal_options_map field, of type HashMap<RegionNumber, EncodedWalOptions>, representing the wal options allocated for each region of a table. When persisting the metadata of a table, the procedure manager also persists the wal options. The EncodedWalOptions is simply a string.

• When the Datanode starts, it reads the persisted DatanodeTableValue from the kv backend, retrieves the wal_options_map, decodes and extracts the wal options for each region. These wal options are stored in RegionOpenRequest for use when opening a region.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #2933 (d8ef9bc) into develop (9af9c02) will increase coverage by 0.67%.
Report is 12 commits behind head on develop.
The diff coverage is 84.64%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2933      +/-   ##
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+ Coverage    85.12%   85.79%   +0.67%     
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  Files          756      767      +11     
  Lines       120101   123627    +3526     
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+ Hits        102232   106065    +3833     
+ Misses       17869    17562     -307     

[WenyXu]

Rest LGTM