Various Updates

[cicdw]

PR Checklist:

• add a short description of what's changed to the top of the CHANGELOG.md
• add/update tests (or don't, for reasons explained below)

Describe this PR

This PR:

• disables the Cancel button for flow runs in a Cancelling state (i.e., those runs for which this button has already been pressed)
• removes Email from the Cloud Hook options for Server users (because it is not present in Server)
• removes references to Flow Run version - this is for tidiness; this version in particular is not very useful, and we should look to display state history graphs in its place

[znicholasbrown]

LGTM @cicdw 🥳