Re-add service level objectives support

[phillip-dd]

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What does this PR do?

• This re-introduces SLO support (originally introduced in add service level objectives support #188 and then reverted in Revert "add service level objectives support (#188)" #198 due to ruby1.9 compatibility issues).
• Original ticket: MA-434

Description of the Change

• This PR addresses the 1.9 compatibility issues.
• Adds a "poor man's hash without indifferent access" to keep the method APIs manageable while also not forcing library users to remember to use string or symbol keys

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[zippolyte]

What's the reasoning behind this one ?
We already have a few endpoints that use a hash for options, but aren't using this symbolized access.

[phillip-dd]

Looking across the other usages, all of the other options are merged into the body without modification. In a few cases here we construct a deeper object in the body based on the flat options passed in.