[Metric threshold rule] Adds new context variable for group by keys

[benakansara]

Summary

Closes #141496

Adds new context variable called groupByKeys which holds object of group by keys for Metric threshold rule.

Manual Testing

1. Create Metric threshold rule with group by e.g. host.name, host.network.name
2. Define action template with context.groupByKeys
3. Wait for alerts to be generated
4. Notice the group by object to be included in the alert notification

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)

[jennypavlova]

LGTM on the Metrics Explorer page - I was able to create a rule there, see the alerts and see the groupByKeys in the rules_types response. Please let me know if there is anything else I need to check there.

[benakansara]

LGTM on the Metrics Explorer page - I was able to create a rule there, see the alerts and see the groupByKeys in the rules_types response. Please let me know if there is anything else I need to check there.

Great, by rules_types response, do you mean alert notification? Then that's enough.

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 38ec756

Metrics [docs]

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	59	65	+6
osquery	109	115	+6
securitySolution	443	449	+6
total			+20

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	68	74	+6
osquery	110	117	+7
securitySolution	520	526	+6
total			+21

History

• 💔 Build #90334 failed c17a04b
• 💚 Build #89617 succeeded c73990f
• 💚 Build #89581 succeeded 861099e
• 💚 Build #89151 succeeded 0cfe195
• 💔 Build #89134 failed 9c08cd9

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[kdelemme]

Tested locally and work as expected 👍🏻 Good job @benakansara