feat(e2e): add wp-env-config-path and playwright-cmd inputs

[Hug0-Drelon]

What?

• Create wp-env-config-path to optionally pass a specific wp-env config file.
• Create playwright-cmd to optionally pass a specific Playwright command (useful for non-usual config).

Why?

Callers need to override the default wp-env discovery and Playwright npm script without forking the composite action.

How?

• Add the two optional inputs with defaults that preserve current behavior.
• Pass --config to wp-env start when wp-env-config-path is set.
• Run ${{ inputs.playwright-cmd }} instead of a hard-coded npm run test:e2e.

Split from #17 (inputs only; cache improvements follow in a separate PR).

Test plan

• Run the e2e action without the new inputs — behavior matches main.
• Pass wp-env-config-path to a custom config and confirm wp-env start -- --config=… is used.
• Pass playwright-cmd to a custom command and confirm that command runs.

Warning

This requires to migrate consumer projects to @wordpress/env 11.

[Hug0-Drelon]

Note: reverted the accidental merge of #20 into this branch. #20 will be reopened against main separately so inputs and cache stay independent.