playground: Add --dry-run for preparing binaries in CI

[breezewish]

What problem does this PR solve?

Sometimes we want to prepare binaries but do not run them. For example, we may want to prepare the binaries in a Docker build step, so that when image is used later (like in CI) there will be no repeated downloads.

What is changed and how it works?

This PR introduce --dry-run exactly for this kind of purpose.

When playground is called with --dry-run, everything will be as usual except that no instance will be run actually, and TiUP playground will stop immediately after everything is prepared.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

$ bin/tiup-playground nightly --dry-run
The component `pd` version v8.5.0-alpha-nightly is not installed; downloading from repository.
download ...
Start pd instance: v8.5.0-alpha-nightly
The component `tikv` version v8.5.0-alpha-nightly is not installed; downloading from repository.
download ...
Start tikv instance: v8.5.0-alpha-nightly
The component `tidb` version v8.5.0-alpha-nightly is not installed; downloading from repository.
download ..
Start tidb instance: v8.5.0-alpha-nightly
The component `prometheus` version v8.5.0-alpha-nightly is not installed; downloading from repository.
download ...
The component `tiflash` version v8.5.0-alpha-nightly is not installed; downloading from repository.
download ...
Start tiflash instance: v8.5.0-alpha-nightly

• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

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