Prevent service config from always running in headless mode when using root flags

[thomaspanf]

In urfave-v3, c.NumFlags() on a subcommand counts all the flags in the hierarchy, including root flags.

If you are using native mode (-c and -d root flags) or use a custom config path (using the -c root flag), the TUI will not launch because c.NumFlags() in urfave-v3 counts the root flags.

before this fix:

staker@node:~/dev/smartnode/rocketpool-cli$ rp5 service config

after:

staker@node:~/dev/smartnode/rocketpool-cli$ rp5 service config
(TUI launches) 

[github-actions]

Coverage Report

[github-actions]

Coverage Report

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/rocket-pool/smartnode/rocketpool-cli/service	0.00% (ø)

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/rocket-pool/smartnode/rocketpool-cli/service/commands.go	0.00% (ø)	935	0	935

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.