docs: add ChangeDetectionStrategy.Eager to Autocomplete examples

[msmallest]

The documentation examples were made when Zone.js and Eager change detection were default. This has caused issues, see issue: #33443.

Explicitly adding changeDetection: ChangeDetectionStrategy.Eager to StackBlitz examples is one key piece needed in the current times. Until a sweep through all the examples makes them compatible with both new change detection defaults.

On the scale of: PR to make everything zoneless + OnPush default compatible > PR to make all examples have zone + Eager for now> make one PR to provide zone and separate PR for various component examples for now, I assume the last one like this PR is the most realistic.

This is the first of my proposed "separate PR for various component examples for now" plan. Provided there are no objections, I am just going to go down the line alphabetically in individual PRs.

edit: the zone provider PR: #33449

edit: I will not open more PRs unless I get maintainer approval

[msmallest]

As per some updates in the respective issue, I was too harsh on the overall state of the compatibility. Sorry.. There is still plenty to be updated, but not as many as I thought. I thought it was better for a bandaid fix first rather than propose a huge chunk of changes with more comprehensive scope, but I think there is a limited enough slice of them that they can be fixed outright in a PR or a few split up ones.

Additionally, autocomplete was already in a solid state where only one example needs a change: https://gist.github.com/michael-small/3b04460a8e9bcb114cf0aeb05f447b91. I picked autocomplete as the first alphabetical, but it does not need as many changes as other ones.