Fix hardcoded ID for Head of Household relationship

[mattwire]

Overview

As identified by @demeritcowboy in #15103 which needs merge first.

Before

Hardcoded ID which isn't always the correct ID.

After

ID which is always the correct ID.

Technical Details

We dont have pseudoconstant on relationshiptype so using API getvalue.

Comments

Ping @demeritcowboy

[civibot]

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[demeritcowboy]

Just noting I probably won't be the best tester for this because the main (maybe only?) use of the primary_contact field seems to be during batch membership/contribution entry. Fixing this might cause some things to come up there.

[eileenmcnaughton]

@mattwire the only is merged so this gets a rebase?

[eileenmcnaughton]

I think this is correct