Add tutorial for creating custom executors

[shrijitsingh99]

No description provided.

[kunaltyagi]

Please format the cpp file (eg: std::cout << notice the added spaces between different literals)

Also, CMakeLists.txt is missing

[SergioRAgostinho]

Is there any location at the moment to where we can point the reader for additional info?

[shrijitsingh99]

The idea was to link them to the design document and Code API.
Both are yet to be merged.

[kunaltyagi]

Create an issue to link them (in your fork or PCL) so we don't forget

[SergioRAgostinho]

Is this forward declaration required? What happens if you move the is_executor_available after the class is defined?

[shrijitsingh99]

It is needed since we check for this inside the class:

static_assert(is_executor_available_v<omp_executor>, "OpenMP benchmark executor unavailable");

[SergioRAgostinho]

That static assert checks for omp_executor, not omp_benchmark_executor

[shrijitsingh99]

Oops. Fixed now.

[shrijitsingh99]

Made the requested changes.

Rendered Preview

[kunaltyagi]

Create an issue to link them (in your fork or PCL) so we don't forget

[kunaltyagi]

LGTM

Tutorial and code are simple enough :)

[SergioRAgostinho]

again. Do not merge until executors are merged into the main repo