headertest: Consider unifying constructors for header generation and adding opts

[renaynay]

We currently have a few different ways to construct header test suite for generating headers whereas we could just unify them into a single constructor NewTestSuite and allow variadic amount of opts, like WithTimestampSpacing to set parameters on the test suite.

Lower priority, but would clean things up even further.

Related to https://github.com/celestiaorg/celestia-node/pull/4032

[Hadijp99]

Good

[crStiv]

@renaynay i've made a PR, could you pls check it out when you'll have a free time