Standard/reusable CLI flags

### What problem are you facing?

Each function author today copies CLI boilerplate (mainly flags, environment variables, and defaults) from the function templates (Go, Python, TS). This leads to eventual inconsistency across functions (env var names drift, each author may decide, e.g. GRPC_MESSAGE_SIZE vs MAX_RECV_MESSAGE_SIZE), some functions miss env tags entirely (e.g. DEBUG), etc.

On top of that, there's no single source of truth and when new standard option is added or a default changes, every function must be updated independently. There is no mechanism to propagate changes.

Standardization of CLI arguments/env variables might become useful for 3rd party tooling (e.g. crossplane-diff) which may need to flag all functions in the composition pipeline at the same time (e.g. programmatically raise the max GRPC size in all functions).

### How could this Function help solve your problem?
Move the standard CLI definition into the SDK, in order to eliminate copy&paste and give authors a single import.