docs: siren docs improvement

[mabdh]

This is rebased to PR #136

Changes

• Update docs
  • Add a glossary section to introduce all key terms.
  • Update concept section to explain all keys terms in details.
  • Update guide flow wth an example journey. Check buf guide for reference.
  • Complete reference to other things should move to references. Check Buf for reference.
  • Update guides to accommodate CLI and API using docusaurus tabs.
  • Create a full CLI reference and move it to reference section.
  • Create a full API reference and move it to reference section.
  • Remove empty pages. Merge monitoring, deployment and troubleshooting in deployment guide only.
• Refactor and clean up codes
• Fix inconsistencies

[coveralls]

Pull Request Test Coverage Report for Build 3297789086

• 79 of 145 (54.48%) changed or added relevant lines in 13 files are covered.
• 8 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 81.17%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/receivers/httpreceiver/receiver_service.go	3	4	75.0%
plugins/receivers/slack/notification_service.go	5	6	83.33%
plugins/receivers/pagerduty/receiver_service.go	4	6	66.67%
plugins/receivers/slack/receiver_service.go	4	6	66.67%
internal/api/v1beta1/receiver.go	2	6	33.33%
core/receiver/type.go	0	6	0.0%
plugins/receivers/httpreceiver/notification_service.go	3	11	27.27%
plugins/receivers/file/receiver_service.go	13	22	59.09%
plugins/receivers/pagerduty/notification_service.go	3	15	20.0%
plugins/receivers/file/notification_service.go	22	43	51.16%

Files with Coverage Reduction	New Missed Lines	%
plugins/receivers/httpreceiver/notification_service.go	1	66.67%
plugins/queues/inmemory/queue.go	7	51.85%

Totals
Change from base Build 3297745307:	-0.2%
Covered Lines:	2996
Relevant Lines:	3691

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💛 - Coveralls