Support passing a custom truststore

[NipunaMadhushan]

Purpose

This will let the user configure a custom truststore via environment variables given below.

BALLERINA_CA_BUNDLE
BALLERINA_CA_PASSWORD
BALLERINA_CA_CERT

Fixes #384

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Certification

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• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes/no

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[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot
E Security Rating on New Code (required ≥ A)

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