fix: Overlong agentName error from GitHub

[QuinnyPig]

Ran into an issue where my org name + project name were 66 characters; GitHub errors if it's more than 64. This truncates that edge case at the cost of a couple bits of entropy from a UUID.

[kichik]

This will break the delete task. That means the runner can stay after Lambda times out or fails for another reason. We may need to use a step to trim it or just trim everywhere it's used.

[QuinnyPig]

Yeah, it looks like right around here is where it should get fixed if truncating it everywhere is the solution:

cdk-github-runners/src/lambdas/delete-runner/index.ts

Line 37 in 84737fb

const runnerId = await getRunnerId(octokit, event.owner, event.repo, event.runnerName);

My JS-foo is weak here.

[QuinnyPig]

Ran it down and applied it everywhere I found it being used. Tested working here.