Add documentation on auth types and environment variable config usage

[miketalley]

Description and Context

We could use better documentation about the different auth types apiKey, oauth2, and personalaccesskey and also how to set the local environment variables to utilize each of these properly.

For example:
apiKey requires setting HUBSPOT_API_KEY and HUBSPOT_PORTAL_ID
oauth2 requires setting HUBSPOT_CLIENT_ID HUBSPOT_CLIENT_SECRET and HUBSPOT_PORTAL_ID
personalaccesskey requires setting HUBSPOT_PERSONAL_ACCESS_KEY HUBSPOT_REFRESH_TOKEN and HUBSPOT_PORTAL_ID

Also some more info on how to use environment variable configs.

Who to Notify

@PaulJKim

[techieshark]

Perhaps especially relevant now that hubspot has deprecated API keys

https://developers.hubspot.com/changelog/upcoming-api-key-sunset