Add support for being able to specify the scheme ( e.g. https )

[johnewing1]

Add support for being able to specify the scheme ( e.g. https ) in opentsdb urls

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Description

Fixes #2087

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How has this been tested?

• [x ] New unit test
• [x ] Manual test to verify querying over https

Checklist:

• [x] This contribution follows the project's code of conduct
• [x] This contribution follows the project's contributing guidelines
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules

[neilfordyce]

Looks great. Probably worthy of updates to docs and reference configs in a couple of places:

1. /docs/configuration.md
2. /cmd/bosun/bosun.example.toml
3. /docker/data/bosun.toml

[johnewing1]

Looks great. Probably worthy of updates to docs and reference configs in a couple of places:

1. /docs/configuration.md
2. /cmd/bosun/bosun.example.toml
3. /docker/data/bosun.toml

File 1 is for the legacy 0.5 config, so we should leave that as is. I've updated the other two.