[google_workspace] Link security labs blog post in the readme

[marc-gr]

What does this PR do?

Adds links to the security labs blog series about google workspace and some clarification for the Delegated Account value also in the README.

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.

[elasticmachine]

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

[elasticmachine]

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• Start Time: 2023-04-28T06:56:35.380+0000

• Duration: 25 min 4 sec

Test stats 🧪

Test	Results
Failed	0
Passed	112
Skipped	0
Total	112

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (14/14)	💚
Files	100.0% (14/14)	💚
Classes	100.0% (14/14)	💚
Methods	100.0% (179/179)	💚
Lines	94.469% (4560/4827)	👍 1.005
Conditionals	100.0% (0/0)	💚

[kcreddy]

LGTM

[elasticmachine]

Package google_workspace - 2.6.0 containing this change is available at https://epr.elastic.co/search?package=google_workspace