add unverified-context to credentials

[sm-ghavami]

Closes 69
This PR is going to add support for unverified smtp servers to prefect-email.

Example

from prefect import flow
from prefect.context import get_run_context
from prefect_email import EmailServerCredentials, email_send_message

credentials = EmailServerCredentials(
    username="EMAIL-ADDRESS-PLACEHOLDER",
    password="PASSWORD-PLACEHOLDER",
    smtp_type="STARTTLS",
    unverified_context=True
)
credentials.save("email-server-credentials")

def notify_exc_by_email(exc):
    context = get_run_context()
    flow_run_name = context.flow_run.name
    email_server_credentials = EmailServerCredentials.load("email-server-credentials")
    email_send_message(
        email_server_credentials=email_server_credentials,
        subject=f"Flow run {flow_run_name!r} failed",
        msg=f"Flow run {flow_run_name!r} failed due to {exc}.",
        email_to=email_server_credentials.username,
    )

@flow
def example_flow():
    try:
        1 / 0
    except Exception as exc:
        notify_exc_by_email(exc)
        raise

example_flow()

Screenshots

Checklist

• References any related issue by including "Closes #" or "Closes ".
  • If no issue exists and your change is not a small fix, please create an issue first.
• Includes tests or only affects documentation.
• Passes pre-commit checks.
  • Run pre-commit install && pre-commit run --all locally for formatting and linting.
• Includes screenshots of documentation updates.
  • Run mkdocs serve view documentation locally.
• Summarizes PR's changes in CHANGELOG.md

[desertaxle]

Thank you for your willingness to contribute to prefect-email! The code for this library has been moved to https://github.com/PrefectHQ/prefect/tree/main/src/integrations/prefect-email. Please reopen this PR there if this functionality is still needed!