add pem option to doc (#3786)

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This change describes the option of using a plain-text PEM format
private key for authentication with Snowflake added in
dbt-labs/dbt-snowflake#671.

## Checklist
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- [X] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
and [About
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- [X] Add a checklist item for anything that needs to happen before this
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Checklist:
- [x] The PR dbt-labs/dbt-snowflake#671 needs to
be merged
- [ ] This doc will need to be updated with the dbt-snowflake version
that supports the PEM key option.

website/docs/docs/core/connect-data-platform/snowflake-setup.md

@@ -124,7 +124,7 @@ Along with adding the `authenticator` parameter, be sure to run `alter account s
 
 To use key pair authentication, omit a `password` and instead provide a `private_key_path` and, optionally, a `private_key_passphrase` in your target. **Note:** Versions of dbt before 0.16.0 required that private keys were encrypted and a `private_key_passphrase` was provided. This behavior was changed in dbt v0.16.0.
 
-Starting from [dbt v1.5.0](/docs/dbt-versions/core), you have the option to use a `private_key` string instead of a `private_key_path`. The `private_key` string should be in Base64-encoded DER format, representing the key bytes. Refer to [Snowflake documentation](https://docs.snowflake.com/developer-guide/python-connector/python-connector-example#using-key-pair-authentication-key-pair-rotation) for more info on how they generate the key.
+Starting from [dbt v1.5.0](/docs/dbt-versions/core), you have the option to use a `private_key` string instead of a `private_key_path`. The `private_key` string should be in either Base64-encoded DER format, representing the key bytes, or a plain-text PEM format. Refer to [Snowflake documentation](https://docs.snowflake.com/developer-guide/python-connector/python-connector-example#using-key-pair-authentication-key-pair-rotation) for more info on how they generate the key.
 
 
 <File name='~/.dbt/profiles.yml'>