feat(filesystem source): Define the Filesystem source interface.

[pangzhenzhou]

What's changed and what's your intention?

A simple definition of the filesystem source interface, in our system we consider s3 as part of the filesystem. Currently, the filesystem includes two basic interfaces Directory and EntrySubscriber.

1. Directory defines a limited number of reading operations and the ability to sense changes in the underlying directory files
2. EntrySubscriber defines read operations on a single file.

Compared to other message sources, Directory is like Topic, Entry is like Partition.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #335 (44c2f26) into main (fc24f97) will increase coverage by 0.03%.
The diff coverage is 85.61%.

@@             Coverage Diff              @@
##               main     #335      +/-   ##
============================================
+ Coverage     74.23%   74.27%   +0.03%     
  Complexity     2681     2681              
============================================
  Files           863      864       +1     
  Lines         48830    48991     +161     
  Branches       1591     1591              
============================================
+ Hits          36250    36388     +138     
- Misses        11767    11790      +23     
  Partials        813      813              

Flag	Coverage Δ
java	62.00% <ø> (ø)
rust	79.52% <85.61%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
rust/connector/src/lib.rs	100.00% <ø> (ø)
rust/connector/src/filesystem/file_common.rs	85.61% <85.61%> (ø)
rust/meta/src/storage/metastore.rs	94.48% <0.00%> (-0.66%)	⬇️
rust/storage/src/store.rs	15.00% <0.00%> (-0.52%)	⬇️
rust/meta/src/storage/sled_metastore.rs	96.77% <0.00%> (-0.11%)	⬇️
rust/stream/src/task/stream_manager.rs	52.83% <0.00%> (ø)
...st/stream/src/executor/aggregation/agg_executor.rs	84.96% <0.00%> (+0.75%)	⬆️
rust/stream/src/executor/local_simple_agg.rs	95.49% <0.00%> (+1.11%)	⬆️

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[tabVersion]

LGTM