[ENH] Parameterise the cost function of `dtw` and `adtw` distance measures

[itsdivya1309]

Reference Issues/PRs

Closes: #1874

What does this implement/fix? Explain your changes.

As we discussed on the slack, I've implemented the parameterised DTW and ADTW as private functions to be used in the upcoming Proximity Forest 2.0.

Does your contribution introduce a new dependency? If yes, which one?

Any other comments?

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[hadifawaz1999]

maybe these can go in distance module as parameter to the original dtw based functions ? not saying in this PR as i know its only used for PF2 for now, but future perspective, what do you think @chrisholder ? however we should have a discussion on how it can affect BA stuff (some math related stuff if we go into this as a general parameter)

[MatthewMiddlehurst]

FYI there were some large conversations regarding this in the core_devs and distances Slack channels. It is not really compatible with the way those functions are currently set up, best to take a look at there.

For now we will do it like this just to move things forward.

[MatthewMiddlehurst]

I assume these are the same functions as your previous changes, but just in a new fine @itsdivya1309? If so I dont really see any issue for now.

[itsdivya1309]

I assume these are the same functions as your previous changes, but just in a new fine @itsdivya1309? If so I dont really see any issue for now.

Yes, that's right.

[MatthewMiddlehurst]

replaced by #1978