Add multi attribute support

[Mrod1598]

Description:
Adds support for multiple attributes through expanding on the otel.instrument signatures.

Existing Issue(s):
#136

Testing:
Added to InstrumentHelperTest

[rmfitzpatrick]

@Mrod1598 thanks for this. I think the implementation seems ok so it would be helpful to update the docstrings and readme to advertise the new signature(s) along with the changes.

[Mrod1598]

@Mrod1598 thanks for this. I think the implementation seems ok so it would be helpful to update the docstrings and readme to advertise the new signature(s) along with the changes.

I'm wording if it's redundant to add all new signatures for all of the signatures added. Do you think it's fine to add a note about here that says that attributes can be swapped out with the Map<String,Map<String,Closure>>?

[rmfitzpatrick]

I'm wording if it's redundant to add all new signatures for all of the signatures added. Do you think it's fine to add a note about here that says that attributes can be swapped out with the Map<String,Map<String,Closure>>?

I think it'd preferable to follow the existing pattern of the showing the instrument signature variations and introduce the new mbean attribute label function map with an example like is done with the labelFuncs. I think the whole thing could be done in 5 lines new or so.

In cases where you'd like to share instrument names while creating datapoints for multiple MBean attributes...

- `otel.instrument(MBeanHelper mBeanHelper, String instrumentName, String description, String unit, Map<String, Closure> labelFuncs, Map<String, Map<String, Closure>> attributeLabelFuncs, Closure instrument)`

<... description and example of attributeLabelFuncs with intended purpose... >

`otel.instrument()` provides additional signatures to allow this more expressive MBean attribute access:
- `otel.instrument(MBeanHelper mBeanHelper, String name, String description, String unit, Map<String, Map<String, Closure>> attributeLabelFuncs, Closure instrument)` - `labelFuncs` are empty map.
- `otel.instrument(MBeanHelper mBeanHelper, String name, String description, Map<String, Map<String, Closure>> attributeLabelFuncs, Closure instrument)` - `unit` is "1" and `labelFuncs` are empty map.
- `otel.instrument(MBeanHelper mBeanHelper, String name, Map<String, Map<String, Closure>> attributeLabelFuncs, Closure instrument)` - `description` is empty string, `unit` is "1" and `labelFuncs` are empty map