Loading state for "Checkout Source Branch" button

[mkenchugonde]

Customer Problem

The 'Checkout source Branch' button in the Pull Request view doesn't have a loading state, and it gives the impression that nothing is happening, and suddenly, it changes to 'Source branch Checkout out.'

This PR will add a loading state to the 'Checkout source Branch' button, which will help to ensure that the checkout is in progress instead of clicking the button multiple times.

Loom Video: https://www.loom.com/share/c58dda9fb5bd494f979cbd940a955f6a?sid=43894cfe-7c32-4438-ad13-cbabec5ec227

[atlassian-cla-bot]

Thank you for your submission! Like many open source projects, we ask that you sign our CLA (Contributor License Agreement) before we can accept your contribution.
If your email is listed below, please ensure that you sign the CLA with the same email address.

The following users still need to sign our CLA:
❌mkenchugonde

_{Already signed the CLA? To re-check, try refreshing the page.}

[sdzh-atlassian]

Hi @mkenchugonde! Thanks for the PR :)

I'm assuming you're a colleague; not sure why it's complaining about the CLA issue - but it's most likely because you're not part of atlassian github org 🤔

IIRC there's a self-serve way of linking your account outlined in Confluence - but if that doesn't help, please feel free to hit me up on Slack, or raise it with #opensource

[sdzh-atlassian]

Looks good to me! ;)

[bwieger-atlassian-com]

Hi,

For all PRs, could you help us by:

1. Visual demostrating the change (loom video / before-after pictures)
2. Lining this up to a customer problem

[mkenchugonde]

Hi,

For all PRs, could you help us by:

1. Visual demostrating the change (loom video / before-after pictures)
2. Lining this up to a customer problem

Hi @bwieger-atlassian-com I have updated the PR description. Thanks for the review.

[bwieger-atlassian-com]

Thank you!

FYI (No Action Required): My UX review in a loom: https://www.loom.com/share/6f8b427f9cbb4014a3a7fe1d34af3a34?sid=6ac8adc1-47a5-4fc1-887d-1c88e0010130