Fix missing unit in Gauge metrics snippet

[rzgry]

Adds unit to the @Gauge snippet since it is required https://github.com/eclipse/microprofile-metrics/blob/master/spec/src/main/asciidoc/app-programming-model.adoc#gauge

All others provide a default value so it is not needed. https://github.com/eclipse/microprofile-metrics/blob/master/spec/src/main/asciidoc/app-programming-model.adoc#fields

[fbricon]

"Fix missing comma"?

[rzgry]

This PR adds the unit attribute in the @Gauge annotation snippet since it was missing: "\tunit = $3",. The added comma in the first line is needed just to add the new attribute.

[angelozerr]

unit is a string, so I think it should be

"\tunit = \"${3:unit}\"",

no?

[rzgry]

I think for the majority of use cases the MetricUnit constants are used. https://github.com/eclipse/microprofile-metrics/blob/master/api/src/main/java/org/eclipse/microprofile/metrics/MetricUnits.java#L34

Ex. from https://quarkus.io/guides/microprofile-metrics
@Gauge(name = "highestPrimeNumberSoFar", unit = MetricUnits.NONE, description = "Highest prime number so far.")

So i didn't want to wrap the placeholder in quotes if they would need to remove them to use the MetricUnit constants.

I would think we leave it as is, or maybe change it to something like: "\tunit = ${3:\"unit\"}",?

[angelozerr]

Snippets should generate code without syntax error, that's why I wonder why it misses quote, but I understand your point of view. So I suggest that you use snippet choice https://microsoft.github.io/language-server-protocol/specification#choice which provides MetricUnits.NONE, and other value of MetricUnits and double quote.

[rzgry]

Updated to use the choice syntax. I only added a couple options. Not sure if we should cover all possible MetricUnits
options? Seems like it might be too much.

[angelozerr]

I think it's nice now because snippets generates annotation without syntax error. Thanks @rzgry !