Do not require -p when using %p in rpk topic produce

[xxchan]

Who is this for and what problem do they have today?

It is confusing that this flag's value is not used, but changes the format's behavior.

❯ rpk topic produce mytopic -f "%p %v\n"     
1 a
Produced to partition 0 at offset 6 with timestamp 1712567714375.
2 b
Produced to partition 0 at offset 7 with timestamp 1712567716705.
3 c
Produced to partition 0 at offset 8 with timestamp 1712567722342.
^C

❯ rpk topic produce mytopic -f "%p %v\n" -p 1
1 a
Produced to partition 1 at offset 17 with timestamp 1712567729382.
2 b
Produced to partition 2 at offset 3 with timestamp 1712567730481.
3 c
Produced to partition 3 at offset 4 with timestamp 1712567731884.

What are the success criteria?

Why is solving this problem impactful?

Additional notes

JIRA Link: CORE-2175