Add new addons to Qiskit addons overview page (#4047)

Add upcoming addons to Overview page and link out to their public repos.
Closes #4031. Do we need to wait for more docs to be be available in the
public repos before publishing here?

Tagging @caleb-johnson @jyu00 @mrossinek, per @kaelynj

---------

Co-authored-by: aeddins-ibm <60495383+aeddins-ibm@users.noreply.github.com>
Co-authored-by: Kaelyn Ferris <43348706+kaelynj@users.noreply.github.com>

Author: 3 people

docs/guides/addons.mdx

@@ -3,6 +3,8 @@ title: Qiskit addons
 description: Understand the Qiskit addon tools, which help you build utility-grade quantum workflows.
 ---
 
+{/* cspell:ignore lightcones */}
+
 # Qiskit addons
 
 Qiskit addons are a collection of research capabilities for enabling algorithm discovery at the utility scale. These capabilities build on Qiskit's performant foundation of tools for creating and running quantum algorithms. They are provided as modular software components that can plug into a [workflow](/docs/guides/intro-to-patterns) to scale or design new quantum algorithms.
@@ -24,6 +26,14 @@ Multi-product formulas (MPF) reduce the Trotter error of Hamiltonian dynamics th
 - Visit the [GitHub repository.](https://github.com/Qiskit/qiskit-addon-mpf)
 - Read the [documentation.](https://qiskit.github.io/qiskit-addon-mpf)
 
+### Optimization mapper
+
+The Optimization Mapper addon contains functionality to model optimization problems by formulating them in abstract models and then converting into representations that a quantum computer can understand.
+
+- Read the [documentation](https://qiskit.github.io/qiskit-addon-opt-mapper/) for how-to guides and API references.
+- Visit the [GitHub](https://github.com/qiskit/qiskit-addon-opt-mapper) repository.
+
+
 ## Addons for optimizing
 
 ### Operator backpropagation
@@ -50,3 +60,32 @@ Sample-based quantum diagonalization (SQD) classically post-processes noisy quan
 - Visit the [GitHub repository.](https://github.com/Qiskit/qiskit-addon-sqd)
 - Read the [documentation.](/docs/guides/qiskit-addons-sqd)
 - Read the tutorial on [Sample-based quantum diagonalization of a chemistry Hamiltonian.](/docs/tutorials/sample-based-quantum-diagonalization)
+
+### SQD for HPC
+
+This addon is an HPC-ready implementation of the SQD addon. It is written in modern C++17 standards and is designed to create a single compiled binary for use with MPI.
+
+- Visit the [API reference](https://qiskit.github.io/qiskit-addon-sqd-hpc/) documentation.
+- View the [GitHub](https://github.com/qiskit/qiskit-addon-sqd-hpc) repository.
+
+## Addons for error mitigation
+
+### M3 (mthree)
+
+Matrix-free Measurement Mitigation (M3) is a package for scalable quantum measurement error mitigation that can be computed in parallel.
+
+- Visit the [documentation](https://qiskit.github.io/qiskit-addon-mthree/) for how-to guides, tutorials, and API references.
+- Visit the package's [GitHub](https://github.com/Qiskit/qiskit-addon-mthree) page.
+
+### Shaded lightcones
+
+The shaded lightcones addon uses Pauli propagation to reduce the number of error terms in a noise model that need to be mitigated, according to the specifics of the target observable. This has the effect of reducing the sampling overhead for probabilistic error cancellation (PEC) workflows.
+
+- Visit the [documentation](https://qiskit.github.io/qiskit-addon-slc/) for how-to guides, tutorials, and API references.
+
+
+### Propagated noise absorption
+
+Propagated noise absorption (PNA) uses Pauli propagation to absorb information from a noise model into a target observable. Measuring this modified observable has the effect of mitigating the noise as represented by the model.
+
+- Visit the [documentation](https://qiskit.github.io/qiskit-addon-pna/apidocs/qiskit_addon_pna.html) for how-to guides, tutorials, and API references.