feature: case-insensitive "digger" in comment ops

[dannysauer]

I wasn't paying attention while working on mobile, and my phone keyboard defaults to upper-casing the first letter typed in a field like it's a sentence, which isn't valid. It's a trivial thing, but perhaps the comment prefix could be compared with case-insensitivity. That may be as simple as updating this line: https://github.com/diggerhq/digger/blob/bbc19311d2c1c18771befb208c14f706321df5ce/backend/controllers/github.go#L738

[dannysauer]

Looks like the command parser is already forcing to lowercase. https://github.com/diggerhq/digger/blob/bbc19311d2c1c18771befb208c14f706321df5ce/libs/scheduler/utils.go#L26-L42