Update INSTALLATION.md to include a workaround for installation on macOS

[StormGear]

Installation on macOS may show a different dialog from the one specified in the INSTALLATION.md currently, I modified the INSTALLATION.md file to include this.

PR Description

Installation on macOS may show a different dialog when one tries to open it. In this PR, I modified the INSTALLATION.md file to include steps to bypass this dialog and finally get API Dash installed on their machine.

Related Issues

• Closes MacOS Installation Roadblock and Adding APIDash Project on Melos #517

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

We encourage you to add relevant test cases.

• Yes
• No, and this is why: This is not a code contribution, it's a contribution to the docs

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux

[ashitaprasad]

Thanks for the PR.