Add parkwalker volunteer role

[fraz3alpha]

• Merge in changes from https://github.com/fraz3alpha/running-challenges/pull/364
• https://blog.parkrun.com/uk/2022/09/26/parkwalker-role-explained/
• Add remaining bits to add the badge
• For https://github.com/fraz3alpha/running-challenges/issues/363

[fraz3alpha]

https://github.com/fraz3alpha/running-challenges/actions/runs/4758385362 has run, and it seems to suggest that the test to check the parkwalker badge is on every profile works, and lo, it works, and you can see the re-coloured other hi-viz too

The parkwalker shouldn't be off at the end thought, so I'll move it up with the others

[fraz3alpha]

There we go, they are together now