feat: ask before apify push drops a Git source

[l2ysho]

Note

TL;DR — apify push on a Git-sourced Actor version now says what it is about to drop and asks before it switches the source to the local files. --force answers yes. Without a terminal and without --force, the push stops.

Closes #1142.

What happened before

apify push set the version's sourceType to SOURCE_FILES without a word. The Git connection and its build setup were gone before anyone noticed, and the platform kept building from the uploaded files. See the issue comments for the agreed shape of the prompt.

What changed

• The version is fetched before the upload, not after. When its source type is GIT_REPO, the command prints a warning with the repository URL, points at git push as the way to build from the repository, and asks:

  Warning: Actor my-scraper builds from a Git repository: git@github.com:apify/my-scraper.git
  A push replaces that source with the local files and drops the Git connection.
  To build from the repository, run git push instead. The platform builds on push when Automatic builds are on.
  ? Switch the source to the local files? (y/N)
  

  The question comes after the "modified on the platform" check, so nobody confirms a push that is about to be refused anyway.

• No stops the push before anything is uploaded. The Actor is untouched.

• --force skips the question but keeps the warning. Its description now covers both cases it overrides: a newer remote version, and a Git source.

• Non-interactive runs without --force stop with an error that names the flag. This is a behavior change for CI pipelines that push to a Git-sourced Actor. Such a pipeline is replacing the repository source on every run, so it should say so explicitly.

• Source-files and tarball versions are not affected. No prompt, no new output.

The second half of the issue

"After switching back to Git, Automatic builds could not be enabled." The API only $sets the keys it receives, so apify push leaves gitRepoUrl and githubWebhookId on the version and flips sourceType only. Whether Console then re-creates the version fields on switch-back is a platform question. Not touched here, and the prompt above removes the usual way into it.

Relation to #1377

#1377 turns Automatic builds on for Actors that apify create --source <provider> makes. This PR is independent of it and applies on master. The warning text says "when Automatic builds are on" rather than promising a build, since a Console-created Actor may have them off.

Verification

lint, format, build, test:local clean. docs/reference.md regenerated for the --force description.

7 new tests in test/local/commands/push-git-source.test.ts, with the platform client mocked: the non-interactive stop leaves the version untouched and names --force; no leaves it untouched; yes and --force switch the source to SOURCE_FILES, and --force never reaches the prompt; source-files and tarball versions neither ask nor warn.

Not run live against a real Git-sourced Actor yet. Draft until that is done.

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[patrikbraborec]

@szaganek please can you review the message?