[Themes] Replace legacy flag in Push command

[jamesmengo]

WHY are these changes introduced?

https://github.com/Shopify/develop-advanced-edits/issues/374

WHAT is this pull request doing?

1. Remove password flag as entrypoint to Legacy implementaiton
   2)legacy renders a warning and direct users to open an issue
2. Introduces a fallback legacy altnerative

How to test your changes?

1. Run the command with the legacy flag

• Should render a warning and run the TS implementation

2. Run the command with a password provided from the theme access app

• Should run the TS implementation

3. Run the command with legacy-3.66

• Should run the Ruby implementaiton

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

cc: @Shopify/advanced-edits

[github-actions]

We detected some changes at either packages/*/src or packages/cli-kit/assets/cli-ruby/** and there are no updates in the .changeset.
If the changes are user-facing, run "pnpm changeset add" to track your changes and include them in the next release CHANGELOG.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	72.62%	8369/11525
🟡	Branches	69.13%	4114/5951
🟡	Functions	71.94%	2190/3044
🟡	Lines	72.92%	7912/10850

Test suite run success

1904 tests passing in 865 suites.

Report generated by 🧪jest coverage report action from 07468e1

[karreiro]

Thank you for this PR, @jamesmengo! LGTM and works as expected for both legacy variations (with and without the --password flag) 🎩