[refactor] Implicitly enable Jira integration via API key

[constantincerdan]

Removes the need to explicitly enable Jira integration via the JIRA_INTEGRATION_ENABLED env variable by implicitly enabling it if the JIRA_API_KEY env variable is provided.

[anno-bot]

This PR may contain the following bugs:

1. Model Name Error:

export CHAT_GPT_MODEL=gpt-4o-2024-08-06

The model name contains a typo - it uses 'o' instead of '0'. The correct format should be 'gpt-40-2024-08-06'.

2. Future Date in Model Names:

export CHAT_GPT_MODEL=gpt-4o-2024-08-06
export CLAUDE_MODEL=claude-3-5-sonnet-20241022

Both model names contain future dates (2024) which don't exist yet, making these model identifiers invalid for current use.

3. Potential Missing Validation:

let jira_enabled = config::get_optional("JIRA_API_KEY").is_some();

The code only checks if the JIRA_API_KEY exists but doesn't validate if other required Jira configurations (JIRA_BASE_URL, JIRA_PROJECT_KEY) are present when Jira is enabled, which could lead to runtime errors.