Remove ios_add2app Pods directory and add to gitignore

[jmagman]

Description

Don't track Pods directory in the ios_add2app integration test.

Related Issues

Fixes #33766.

Tests

I ran ios_add2app integration test ./build_and_test.sh, all tests passed.

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (Please read [Handling breaking changes]). Replace this with a link to the e-mail where you asked for input on this proposed change.
• No, this is not a breaking change.

[dnfield]

How much time does this add to the test, and can we do anything to make sure it doesn't lead to flakiness?

I included these to try to make the test more hermetic :\

[jmagman]

How much time does this add to the test, and can we do anything to make sure it doesn't lead to flakiness?

I was following in the footsteps of #9464 and #9550. How would it cause flakiness?

The top-level https://github.com/flutter/flutter/blob/master/.gitignore includes **/ios/**/Pods/ so I think the intention was to never check in a Pods directory for any checked in Xcode project, but this integration test doesn't match that pattern.

[dnfield]

Hm. Looking at the test execution, looks like I was wrong about how much time it would add.

The flakiness concern is that we're now downloading and generating more content - but as long as it's not making this test more flaky that's fine with me. We can watch it.

LGTM