Set user-agent to Gutenberg WebView

[marecar3]

This request was failing after login affecting Gutenberg Web View for Unsupported blocks.

Fixes parts of wordpress-mobile/gutenberg-mobile#2358

Example of user-agent that we set to user-agent:
user-agent: Mozilla/5.0 (Linux; Android 10; Pixel 3 Build/QQ2A.200501.001.B2; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/83.0.4103.106 Mobile Safari/537.36 wp-android/alpha-230

To test:

• Have a post on your non-Atomic site ready with an unsupported block.
• Log out of WPAndroid app.
• Delete the app.
• Build from this PR.
• Run Metro server (to have the Unsupported blocks option available).
• Login and navigate to the post with the unsupported block.
• Open the post.
• Open the unsupported block on Gutenberg Web-View.
• Check that it doesn't prompt for login-in.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

cc @aerych

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[khaykov]

I spend some time trying to setup GB environment and I keep getting various errors, I don't have much context about what's going wrong, so It's hard to fix them. I'm going unassign myself, so maybe someone with working environment cant take a look at this PR 🙇

[marecar3]

I spend some time trying to setup GB environment and I keep getting various errors, I don't have much context about what's going wrong, so It's hard to fix them. I'm going unassign myself, so maybe someone with working environment cant take a look at this PR 🙇

Hey @khaykov, could you give it another chance?
I just merge latest develop into this branch which could solve the problem

[khaykov]

I managed to make it work! Thanks for the fix @marecar3 , it works as expected. I was not able to reproduce the issue by removing setUserAgentString. Is there something else I can do to confirm it?

[marecar3]

I managed to make it work! Thanks for the fix @marecar3 , it works as expected. I was not able to reproduce the issue by removing setUserAgentString. Is there something else I can do to confirm it?

Thanks a lot @khaykov for helping with this, that would be all!