What does this PR do?

Add dimensions to firewall, transit gateway and vpn data streams.

Transit gateway: A transit gateway can have more than one attachment, so it needs to be set as dimensions as well. A transit gateway is unique per AWS account.

VPN: Each tunnel belongs to a VPN. Combination tunnel id + vpn id is unique within the AWS scope account (account id + region).
Note: for each VPN site to site connection, there are four documents sent to ES. Is this expected?

Firewall: The firewall name is unique per region in an account. A firewall can have more than one engine and one Availability Zone, so both need to be set as dimension to avoid documents being overwritten. Since we can have more than one custom action in the same firewall, we also set that as dimension.
Question:CustomAction fields holds the name of the action. Since a firewall can have different groups (names are unique, but we don't have access to that field in this data stream), then we can also have different custom actions with the exact same name associated with one firewall. I tried to reproduce this, but even with multiple rules with the same name I kept receiving just one document for each rule. Without considering TSDB, can we receive two documents for the same action at the same time? If so, dimensions are not enough for this data stream.

Regarding ECS fields, more info can be found here#5193 (comment).

Checklist

• I have reviewedtips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package'schangelog.yml file.
• I have verified that Kibana version constraints are current according toguidelines.

Author's Checklist

• Verification of the count of documents (before & after TSDB enablement) in Discover Interface
• Verify if field mapping is correct in the data stream template.

How to test this PR locally

Refer to#6293.

Related issues

Relates to#6293.