OM2.0: Add info and examples for UTF-8

Signed-off-by: Owen Williams <[email protected]>

Author: ywwg

docs/specs/om/open_metrics_spec_2_0.md

@@ -439,6 +439,29 @@ go_goroutines 69
 # UNIT process_cpu_seconds seconds
 # HELP process_cpu_seconds Total user and system CPU time spent in seconds.
 process_cpu_seconds_total 4.20072246e+06
+# TYPE "foodb.read.errors" counter
+# HELP "foodb.read.errors" The number of errors in the read path for fooDb.
+{"foodb.read.errors", "service.name"="my_service"} 3482
+# EOF
+```
+
+##### UTF-8 Quoting
+
+Metric and label names not conforming to the ABNF definition of `metricname` MUST be enclosed in double quotes and the alternative UTF-8 syntax MUST be used.
+Quoting and the alternative metric name syntax MAY be used for any metric name, regardless of whether the name conforms to `metricname` or not.
+The metric names MUST be enclosed in double quotes in TYPE, UNIT, and HELP lines. The metric name MUST be moved inside the brackets without an operator, in accordance with the ABNF.
+Label names not conforming to the `label-name` ABNF definition MUST be enclosed in double quotes. Any label name MAY be enclosed in double quotes.
+
+Complete example:
+
+```openmetrics
+# TYPE "process.cpu.seconds" counter
+# UNIT "process.cpu.seconds" seconds
+# HELP "process.cpu.seconds" Total user and system CPU time spent in seconds.
+{"process.cpu.seconds", "node.name"="my_node"} 4.20072246e+06
+# TYPE "quoting_example" gauge
+# HELP "quoting_example" Number of goroutines that currently exist.
+{"quoting_example", "foo"="bar"} 4.5
 # EOF
 ```
 
@@ -538,6 +561,8 @@ The value of a UNIT or HELP line MAY be empty. This MUST be treated as if no met
 # HELP foo_seconds Some text and \n some \" escaping
 ```
 
+See the UTF-8 Quoting section for circumstances where the metric name MUST be enclosed in double quotes.
+
 There MUST NOT be more than one of each type of metadata line for a MetricFamily. The ordering SHOULD be TYPE, UNIT, HELP.
 
 Aside from this metadata and the EOF line at the end of the message, you MUST NOT expose lines beginning with a #.
@@ -566,6 +591,13 @@ Label values MAY be any valid UTF-8 value, so escaping MUST be applied as per th
 bar_seconds_count{a="x",b="escaping\" example \n "} 0
 ```
 
+Metric names and label names MAY also be any valid UTF-8 value, and under certain circumstances they MUST be quoted and escaped per the ABNF.
+See the UTF-8 Quoting section for specifics.
+
+```openmetrics-add-eof
+{ "\"bar\".seconds.count", "b\\"="escaping\" example \n "} 0
+```
+
 The rendering of values for a MetricPoint can include additional labels (e.g. the "le" label for a Histogram type), which MUST be rendered in the same way as a Metric's own LabelSet.
 
 #### MetricPoint