[semver:minor] add ability to specify version of prom/am tool install binaries

[dgeorges]

SEMVER Update Type:

• Major
• Minor
• Patch

Description:

Allow for the user of the orb to specify which version of the tool to install.

Motivation:

Builds failing to install am tools because of dependencies missing.

installing amtool
/go/src/github.com/prometheus/alertmanager/notify/notify.go:24:2: cannot find package "github.com/cespare/xxhash" in any of:
	/usr/local/go/src/github.com/cespare/xxhash (from $GOROOT)
	/go/src/github.com/cespare/xxhash (from $GOPATH)

This is the cause of breaking changes. Allow for the user of the orb to specify which version of the tool to install.
see: prometheus/prometheus#8480

Closes Issues:

https://jira.onemedical.com/browse/SRE-529

Checklist:

• All new jobs, commands, executors, parameters have descriptions.
• Usage Example version numbers have been updated.

CLA Acceptance

Please indicate your acceptance of the CLA below:

• I ACCEPT -- I have sole ownership of intellectual property rights to my Contribution and I am not making a submission in the course of work for my employer.

• I ACCEPT -- I am making the Contribution in the course of my work for my employer, [EMPLOYER NAME]. I have permission from [EMPLOYER NAME] to make the Contribution under the CLA.