docs: update waiting for app stability recipe for Angular 18

[arturovt]

In this commit, we updated the "waiting for app stability" recipe to use
the experimental pending tasks service, which was publicly exposed in the
Angular API starting from version 18.

[nx-cloud]

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✅ Successfully ran 6 targets

• nx run-many --target=test --all --configuration=ci --base=remotes/origin/master --head=HEAD
• nx lint-types store
• nx run-many --target=lint --all --configuration=ci --base=remotes/origin/master --head=HEAD
• nx run-many --target=build --all
• nx run-many --target=test --all --configuration=ci --maxWorkers=4
• nx run-many --target=lint --all

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[bundlemon]

BundleMon (Integration Projects)

Unchanged files (2)

Status	Path	Size	Limits
✅	Main bundles(Gzip) hello-world-ng17/dist-integration/main.(hash) .js	68.5KB	+1%
✅	Main bundles(Gzip) hello-world-ng16/dist-integration/main.(hash) .js	67.03KB	+1%

No change in files bundle size

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Current branch size history | Target branch size history

[codeclimate]

Code Climate has analyzed commit c1add5c and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 95.5% (0.0% change).

View more on Code Climate.