DBT-772: Upgrade dbt-impala adapter to use v1.6 dbt-core

[vamshikolanu]

Describe your changes

1. Upgrade dbt-core to 1.6
2. Removed support for microseconds datediff micro as Impala doesn't really support microseconds extration from timestamp.
3. Renamed prepare-env to dev_setup in the make file to make it consistent with dbt-hive adapter.

Internal Jira ticket number or external issue link

https://jira.cloudera.com/browse/DBT-772

Testing procedure/screenshots(if appropriate):

https://gist.github.com/vamshikolanu/f6f6800ce24f638d2936addf56101b82

Checklist before requesting a review

• I have performed a self-review of my code
• I have formatted my added/modified code to follow pep-8 standards
• I have checked suggestions from python linter to make sure code is of good quality.

[niteshy]

Few things:

1. Let's land the separate PR for dbt-core 1.5 upgrade, so that we know test fixes are required for 1.6
2. If there are code change then let's put a separate PR so that it is easier to update the release notes.
3. 1.6 upgrade can happen with test fixes.

[niteshy]

Please merge 1.5 PR first, then you can merge it.