fix: add keywords array to plugin.json

[ckbedwell]

Added keywords array to plugin.json and the $schema so we can be made aware of any invalidations moving forwards.

This is needed as the CI/CD check in the release process failed: https://github.com/grafana/synthetic-monitoring-app/actions/runs/22096907179/job/63891288305

(like our ID doesn't match the regex pattern...)

[Pokom]

Looks like most of the diff is from formatting of the json blob, splitting out actions and scopes to multiple lins

[github-actions]

Script size changes

Name	+/-	Main	This PR	Outcome
[217.js]	=	2,190.04 kB	2,190.00 kB	✅
[361.js]	-0.05%	801.47 kB	801.07 kB	✅
[datasource/module.js]	=	25.25 kB	25.25 kB	✅
[692.js]	=	20.64 kB	20.64 kB	✅
[663.js]	=	5.83 kB	5.83 kB	✅
[module.js]	=	4.59 kB	4.59 kB	✅
[156.js]	=	1.90 kB	1.90 kB	✅

Totals

Name	+/-	Main	This PR	Outcome
[Scripts]	-0.01%	3,049.72 kB	3,049.27 kB	✅
[Non-script Assets]	+0.07%	2,677.50 kB	2,679.28 kB	✅
[All]	+0.02%	5,727.22 kB	5,728.55 kB	✅

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