[GCP] Support additional input param in PubSub input for all datastreams

[kcreddy]

What does this PR do?

Adds support for configuring subscription_num_goroutines and subscription_max_outstanding_messages parameters across all datastreams having GCP PubSub input.

Checklist

• I have reviewed tips 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's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

How to test this PR locally

Related issues

• Closes [GCP] | Support num_goroutines and max_outstanding_messages for GCP PubSub datastreams #5629

Screenshots

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2023-03-22T07:37:59.497+0000

• Duration: 17 min 25 sec

Test stats 🧪

Test	Results
Failed	0
Passed	57
Skipped	0
Total	57

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (6/6)	💚
Files	100.0% (6/6)	💚
Classes	100.0% (6/6)	💚
Methods	90.291% (93/103)	👎 -9.709
Lines	96.0% (1464/1525)	👎 -4.0
Conditionals	100.0% (0/0)	💚

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

Package gcp - 2.18.0 containing this change is available at https://epr.elastic.co/search?package=gcp