Add bootnode template, allow configuring base recipe flags through yaml.

[dvush]

Here are the changes to make my custom recipes to work.

1. Add {{Bootnode}} template for YAML recipes
   Enable YAML recipes to reference the bootnode enode URL using {{Bootnode}}
   template. This allows custom services to connect via p2p to the bootnode
   without hardcoding addresses.
2. Add base_args support for YAML recipes
   Allow YAML recipes to pass arguments to the base recipe's flags.
   This enables setting options like --enable-latest-fork for opstack.

The second one allow doing this in custom recipes:

base: opstack
base_args:
  - --enable-latest-fork
  - "0"

I am not sure if its the best approach for this but it works, there should be a way to configure it in some way

[claude]

Claude finished @dvush's task in 2m 9s —— View job

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PR Review Complete

Reviewed the changes adding {{Bootnode}} template and base_args support for YAML recipes.

Summary

The core functionality works correctly for opstack-based YAML recipes. The resolveAddr refactoring is clean and base_args implementation is straightforward.

Issues Found

1. Empty string when Bootnode not configured - Using {{Bootnode}} with base: l1 silently returns empty string since L1 recipe doesn't set ctx.Bootnode. This could cause confusing command-line behavior.

2. Hard-coded "rpc" port name - playground/local_runner.go:421 assumes bootnode service always has a port named "rpc". Custom services with different port names would panic.

3. Missing Bootnode template in manifest.go - While YAML recipes work (they bypass WithArgs()), if a Go component uses {{Bootnode}} in WithArgs(), it will panic during template parsing. Consider adding a pass-through function for consistency.

See inline comments for details.

[claude]

This silently returns an empty string when Bootnode is nil (e.g., when using base: l1). This could lead to confusing behavior where commands have empty values where the enode URL was expected. Consider logging a warning or returning an error indicator so users know something is wrong.

[claude]

Hard-coded port name "rpc" assumes the bootnode service always has this port. If a custom YAML recipe uses a different port name, this will panic via MustGetPort. Consider making the port name part of BootnodeRef or documenting this requirement.