relates to #18326
Add ability to add software from the UI. This includes
- new button on software page to open add software modal
- new add software modal to add software.
> Note: still need to do form error validation but will do on another PR
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality
