Use a regex to match feature branch

[rwb27]

I had some odd issues where the feature branch seemed to contain junk characters at the end.

This PR changes two things:

1. We now match the branch name more robustly with a regex. That should stop us having junk at the end of the string.
2. We no longer use an if condition on check-for-ofm-feature-branch, instead it will just return an empty string. There's now an if condition on the test-against-ofm-feature-branch job. That removes the need for the somewhat unsightly toJSON and \r\n.
3. I use an action, rather than a bash script, to match the regex. This is much nicer, I think - working with multiline variables was pretty cumbersome in bash, and debugging was a pain.

• I've tested the final commit with OFM Feature Branch: verify-ui-elements in the description
• I've tested the final commit without that string in the description

[barecheck]

Barecheck - Code coverage report

Total: 96.34%

Your code coverage diff: 0.00% ▴

✅ All code changes are covered

[rwb27]

For the record, I've tested commit 1c77aeb with and without the relevant string in the description.

[bprobert97]

This looks good. The only potential thing I notice with the regex on line 225 of the YAML is that [\w\-] only captures alphanumeric characters, underscores and dashes, so if anyone uses a slash or a dot in their OFM branch name it won't get picked up.

This isn't a problem necessarily, but might be worth documenting in a contributing.md or readme.md to prevent confusion in future. This would need documenting in LabThings and OFM Server

[bprobert97]

Regex has been updated to allow dots and slashes - happy for this to go in