Do not throw error when analytics are disabled.

[Pruxis]

Imagine the following case where you disable segment in your code.

const { Analytics } = require('@segment/analytics-node');
new Analytics({ writeKey: processe.env.WRITE_KEY || '', disable: true });

If WRITE_KEY is not present, but your analytics are disabled this still throws an error.

This would simplify local setups and do not force them to have a truthy string as write key

[changeset-bot]

🦋 Changeset detected

Latest commit: d25217d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@segment/analytics-node	Patch

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[chrisradek]

@Pruxis Thanks for opening this pull request! I think from a TypeScript perspective writeKey will still be required with this change - @silesky do you think we should update types as well (I think we'd need a tagged union to make this nice) or really just keep this a runtime check?

[silesky]

@Pruxis Thanks for opening this pull request! I think from a TypeScript perspective writeKey will still be required with this change - @silesky do you think we should update types as well (I think we'd need a tagged union to make this nice) or really just keep this a runtime check?

Runtime only; no Typescript changes are needed here IMO.

[Pruxis]

@silesky Do I need to write some tests to get this merged?