Configurable operation timeouts

[turkenh]

Description of your changes

Fixes #176

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

• unit tests
• with provider gcp (WIP)

[muvaf]

Suggested change

	Read *time.Duration
	Create *time.Duration
	Update *time.Duration
	Delete *time.Duration
	Read time.Duration
	Create time.Duration
	Update time.Duration
	Delete time.Duration

I am guessing that you had to use pointers to check whether it's given or not but there is a function (t Time) IsZero() bool we can use to do that. If that's the only reason, we could get rid of TimeDuration(d time.Duration) *time.Duration and work with value types.

[turkenh]

Yes, that was the reason and I was thinking that setting timeout to 0 could be a valid scenario, e.g. no timeout. But digging the terraform sdk code, I noticed that there is no such an implementation and probably no timeout does not make sense at all.

So, I would revert pointers but to check zero value I can not use IsZero() because it is on time.Time not time.Duration. Am I missing something?

Otherwise, I will go with the following:

	if t := fp.Config.OperationTimeouts.Read.String(); t != "0s" {
		timeouts["read"] = t
	}

[muvaf]

Oh yes, I missed that IsZero wouldn't work. I think you can check like fp.Config.OperationTimeouts.Read != 0 since type Duration int64

[muvaf]

LGTM after it's tested manually. Thanks!