[Frontend] Add pennylane.compilers entry points interface

[maliasadi]

For any compiler packages seeking to be registered in PennyLane, this PR adds the entry_points metadata under the the group name pennylane.compilers, with the following entry points:

• context: Path to the compilation evaluation context manager. This context manager should have the method context.is_tracing(), which returns True if called within a program that is being traced or captured.

• ops: Path to the compiler operations module. This operations module may contain compiler specific versions of PennyLane operations. Within a JIT context, PennyLane operations may dispatch to these

• qjit: Path to the JIT compiler decorator provided by the compiler. This decorator should have the signature qjit(fn, *args, **kwargs), where fn is the function to be compiled.

[maliasadi]

@josh146 @dime10 I'm hoping to get this PR merges so that I can check the integration tests in PL against the master branch. This is the only vital update in Catalyst required for the PL-Catalyst integration at the moment.

[dime10]

Looks great my side 💯
I like the 3 objects a compiler must provide 👍

Don't forget to add a changelog!

[dime10]

How is this different from #321?

[josh146]

Thanks Ali!

Don't forget to update the changelog :)

[maliasadi]

@dime10 I created that draft PR to address all changes required for the integration. So far the only requirement was the addition entry points. But we may want to update the signature of Catalyst functions (pennylane_extensions.py) to make them consistent with PL ones.