Introduce alert state and timeouts

[trueleo]

Description

Implement alert state such that webhooks can be called on both alert trigger and alert resolution. Timeouts are also added to avoid flooding targets ( this is opt in rather than opt out because it adds overhead of state check and timer spawn mechanism ). Numeric rule and String rule are used through Consecutive* rule which takes repeat value as 1 if no repeat value is given.

ref to #184

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.

[nitisht]

Tested, looking great!

Few small changes we need

1. Split the rule field into a type and config field. It is easy to understand for the user. We can later add more types like query-based, status-based etc.

	"rule": {
		"type": "column-based", // we'll add more types later
		"config": {
                      "column": "status",
                      "operator": ">=",
                      "value": 500,
                      "repeats": 3
		}
	},

2. Under targets, let's rename timeout --> repeat. server_url --> url.
3. Add validation for repeat field inside the target. If it is not provided, no issues, but if a junk value is sent inside repeat field, server should fail the set alert API.