[Repository] Define and tune for appropriate ThreadPool/Executor usage for multi stream downloads

[kotwanikunal]

Is your feature request related to a problem? Please describe.

• Multi-stream download support was added as a part of Add async blob read and download support using multiple streams #9592
• Currently the streams are downloaded as a part of the GENERIC threadpool which can get overwhelmed in case of large/multiple download requests (kotwanikunal@6765b16#diff-dda04fd83239f00e61a377bf1a17a0f2e8c4a5984eaa539ac46aa2dfae4f5fe7R57)
• This task will focus on defining the appropriate threadpool usage for multi stream downloads

Describe the solution you'd like

• Define a new Executor for multi stream downloads and/or tune the existing usage to prevent over utilization of existing executor

Describe alternatives you've considered

• N/A

Additional context
#9592

[kotwanikunal]

Resolved for now by #10349