specs: mark .cmdline in UKI as optional

[bluca]

The .cmdline section in a UKI is optional in both sd-stub and ukify, so mark it as such in the specification too

[poettering]

migth make sense do say what it is supposed to mean when the .cmdline section is absent, and what the difference to including a .cmdline but setting it to any empty string is. (i.e. that an absent .cmdline means that the cmdline is overridable even in SecureBoot mode).

[bluca]

migth make sense do say what it is supposed to mean when the .cmdline section is absent, and what the difference to including a .cmdline but setting it to any empty string is. (i.e. that an absent .cmdline means that the cmdline is overridable even in SecureBoot mode).

Isn't that more of a sd-stub detail (that we might want to change separately)? ie it's what the loader does, rather than what the image is

[poettering]

Isn't that more of a sd-stub detail (that we might want to change separately)? ie it's what the loader does, rather than what the image is

well, sd-stub implements the logic, but I am pretty sure that the spec should dictate what sections (their presence and their absence) are supposed to mean.

[bluca]

-> #73