Support for custom env var when passing user token in `DBI::dbConnect(odbc::databricks())`

[JavOrraca]

Connecting to a serverless SQL warehouse from a user access token with odbc::databricks() requires setting the Databricks token to a global environment variable named DATABRICKS_TOKEN. If a user has their PAT assigned to the global env var DATABRICKS_TOKEN:

# This works
conn_1 <- DBI::dbConnect(
  odbc::databricks(),
  workspace = "https://some-corp.cloud.databricks.com",
  httpPath = "sql/1.0/warehouse/e123456789101112"
)

# This also works
conn_2 <- DBI::dbConnect(
  odbc::databricks(),
  workspace = "https://some-corp.cloud.databricks.com",
  token = Sys.getenv("DATABRICKS_TOKEN"),
  httpPath = "sql/1.0/warehouse/e123456789101112"
)

However, the code below fails even if DATABRICKS_TOKEN_LAB is set in the .Renviron with the user's correct PAT:

# This fails because token is not specifically calling an env var named DATABRICKS_TOKEN
conn_3 <- DBI::dbConnect(
  odbc::databricks(),
  workspace = "https://some-corp.cloud.databricks.com",
  token = Sys.getenv("DATABRICKS_TOKEN_LAB"), 
  httpPath = "sql/1.0/warehouse/e123456789101112"
)

I work with five (💀) Databricks instances at work so being able to connect to the different endpoints (all w/ different PATs) using different env var names would be very helpful. Thanks!