Enforce RFC 1123 on procfile process types

[joshwlewis]

Kubernetes restricts some resource names to RFC 1123, requiring that names match rules for subdomains. This buildpack produces process types that may be inconsistent with this spec. Notable inconsistencies:

• This buildpack supports capital letters (e.g. Web)
• This buildpack supports underscores (e.g. my_worker)
• This buildpack supports non-alphanumerics at the start or end of the string (e.g. worker2, 2nd-worker)

Process types like these may cause issues when running the build result in a k8s environment, resulting in errors like these:

a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')

We could:

• Coerce the entries to proper casing (downcasing)
• Coerce the entries to use dashes (gsub _ -)
• Write warning messages for non-compliant naming (e.g. "The fast_worker process has an underscore. This may cause problems in kubernetes environments. Consider changing this to fast-worker.")
• Throw errors and fail the build for non-compliant naming

[schneems]

Coerce the entries to proper casing (downcasing)

That seems fine. Issue a warning. Error on duplicate names i.e. Web and weB

Coerce the entries to use dashes (gsub _ -)

Also fine, and issue a warning.

Write warning messages for non-compliant naming (e.g. "The fast_worker process has an underscore. This may cause > problems in kubernetes environments. Consider changing this to fast-worker.")

👍🏻

Throw errors and fail the build for non-compliant naming

I think we try to infer intent when we can. When we can't then we error.