feat: New bootstrap function

[nhhagen]

Bootstrap function that checks for the required configuration and return a
function to stop the Datadog integration.

Closes: #427

[nhhagen]

@bendiknesbo, @hadrienk and @hawi74 here is an early draft of the implementation.

So far the implementation:

• returns a context, cancel func and error
• official Datadog options is set though environment variables, the minimal config is validated if it is present.
• our custom options have default with overloads from environmental variables and functional options, no functional options are implemented to override the options.

We should discuss if the are other ways of ensuring that we can guarantee that the stop functions are called other than returning a cancelable context and a cancel func.

I have not yet looked into metrics as I wanted to get this pattern right first, should we do metrics as a separate PR?

[nhhagen]

@bendiknesbo, @hadrienk, @hawi74 should we introduce metrics improvements in this PR?

Ref:

• Improved metrics API #433

[nhhagen]

I have added an error handler as discussed in #433 (comment)

i was just commenting..

Invalidated by push of 696bcf7

Change request is not applicable