Updated Adapters' iOS Framework to become static libraries

[LTPhantom]

Description

For all Mediation Adapters, updated the podspec file as static libraries. Future release PRs will be done for each adapter later.

Related Issues

#1107

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[orkun1675]

Can we publish pub.dev releases with this PR? Thanks!

For now, in order to get my app to build I'm using:

  gma_mediation_unity: # Unity Ads adapter
    git:
      url: https://github.com/googleads/googleads-mobile-flutter.git
      ref: fe544bf52158ef12dc79392239f74ce1017c4c82
      path: packages/mediation/gma_mediation_unity