Add serverless guide with function template example: hamiltonian simulation

[garrison]

The very rough outline is intact, including the code, but I still need to write/revise some prose between the cells. Right now this example uses the mergedeep package to merge the user's estimator options with the function's default. If we need to remove this dependency, then I will modify the program so that if a user passes estimator options, they completely replace the function's default.

Closes #2242.

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[qiskit-bot]

One or more of the following people are relevant to this code:

• @jenglick
• @pandasa123

[frankharkins]

I'm merging this to a branch in this repo so we can get a preview

[frankharkins]

Please make any follow-up commits to the FH/preview-fct-template branch. If you've accidentally committed to this branch, you can pull your commit over to that branch using:

git switch FH/preview-fct-template
git cherry-pick <your-commit>