Accept gate lists in benchmarking

[chaeyeunpark]

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Context: As a step to add an alternative implementation of kernel, it is good to have a benchmark code testing a given list of gates.

Description of the Change: Examples submodule is now under the main cmake; Benchmark code for a given list of gates added.

Benefits: We can now benchmark some gate operations we give. E.g. we can now

$ ./examples/gate_benchmark_oplist 1000 10 [PauliX, CNOT] # benchmark only PauliX and CNOT
$ LOG=1 ./examples/gate_benchmark_oplist 1000 10 [PauliX, CNOT] 2> gates.log # Same as above but log generated random gates sequence

Possible Drawbacks: I am not aware of any drawbacks.

Related GitHub Issues:

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[codecov]

Codecov Report

Merging #199 (1b9efb3) into master (ab533a0) will not change coverage.
The diff coverage is n/a.

❗ Current head 1b9efb3 differs from pull request most recent head 30865ec. Consider uploading reports for the commit 30865ec to get more accurate results

@@           Coverage Diff           @@
##           master     #199   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files           4        4           
  Lines         278      278           
=======================================
  Hits          277      277           
  Misses          1        1           

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[github-actions]

Test Report (C++) on Ubuntu

       1 files  ±0         1 suites  ±0   0s ⏱️ ±0s
   378 tests ±0     378 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
2 233 runs  ±0  2 233 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 30865ec. ± Comparison against base commit ab533a0.

♻️ This comment has been updated with latest results.

[mlxd]

Great work @chaeyeunpark
I had some tiny comments, but happy to approve once they are answered.