[Docs]: Self-hosted agents page

[TomFern]

Type

New content idea

What do you want to report?

We need a page explaining Self-hosted agents

Code of Conduct

• [X] I agree to follow this project's Code of Conduct

[TomFern]

Review links:

• https://storage.googleapis.com/sem-docs/main/index.html#/docs/using-semaphore/self-hosted
• https://storage.googleapis.com/sem-docs/main/index.html#/docs/using-semaphore/self-hosted-install
• https://storage.googleapis.com/sem-docs/main/index.html#/docs/using-semaphore/self-hosted-configure
• https://storage.googleapis.com/sem-docs/main/index.html#/docs/using-semaphore/self-hosted-aws
• https://storage.googleapis.com/sem-docs/main/index.html#/docs/reference/self-hosted-config

[AleksandarCole]

Amazing work 👏

Added a very small formatting adjustment: https://github.com/semaphoreci/semaphore/pull/155

Please close the ticket after PR review.