[FEATURE] SendGrid - Attachment props

[vunguyenhung]

Is your feature request related to a problem? Please describe.
The current Attachments prop requires user to pass in base64 content, which is really hard for normal user to use

Describe the solution you'd like
Please improve the prop so that the user can put in the list of path to tmp dir, so you can directly use the file in their tmp dir

Do you have a workaround?
Use Code step

Additional context
Reported by a customer here: https://pipedream-users.slack.com/archives/CPTJYRY5A/p1741131818086989

[vunguyenhung]

Hello everyone, I have tested this PR and there're some test cases failed or needed improvement.

Please check the test report below for more information
https://vunguyenhung.notion.site/FEATURE-SendGrid-Attachment-props-1afbf548bb5e8128a13ec43925792ad8