Add ability to choose source branch when creating a new branch from an issue

Description

Add ability to choose which source branch to use when creating a new issue branch. Currently, when creating a new issue branch, you don't get the option to choose which branch to branch from, it uses the project's default branch.

Proposal

It would be great to have a UI element that allows the user to choose which source branch they would like to use when creating a new issue branch.

Links / references

Similar functionality is seen in JIRA. You can create a branch from an issue and choose which branch you'd like to branch from when creating a new branch from an issue.