[*] improve custom_installation.md docs file (#1379)

* Rewrite the `custom_installation.md` docs file

1. Make it clearer and better in structure
2. Reference the grafana docs for grafana installation/setup steps as its better maintained there

* fix typo

Co-authored-by: Mazen Kamal <[email protected]>

* Improve `custom_installation.md`

* remove unsupported Consul and ZooKeeper

* break options into list items

* remove sql and add options for configuring sources

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Co-authored-by: Mazen Kamal <[email protected]>
Co-authored-by: Pavlo Golub <[email protected]>

Author: 3 people