Change metric and label names to get rid of `worker` term if possible

[Envek]

It seems that by mistake I chose the ambigous name worker for use in metric or label names. It led to my confusion several times (e.g. in #11 (comment) or #13 (comment))

Even @mperham recommends against using it in https://www.mikeperham.com/2021/04/20/a-tour-of-the-sidekiq-api/:

…it helps to understand the basic entities in Sidekiq’s universe:

• A job is a unit of work in your Ruby application
• A queue is a list of jobs which are ready to execute right now
• A process is a Sidekiq process with one or more threads for executing jobs.

NB: I never use the term worker as it is nebulous and confusing. Use process, thread or job class so your meaning is clear.

However, this is apparently a breaking change, so we probably should find a trade-off between the passion to name things right and not breaking things too much.

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Code of interest is here:

yabeda-sidekiq/lib/yabeda/sidekiq.rb

Lines 21 to 46 in 91c8f4e

	counter :jobs_enqueued_total, tags: %i[queue worker], comment: "A counter of the total number of jobs sidekiq enqueued."
	next unless ::Sidekiq.server?
	counter :jobs_executed_total, tags: %i[queue worker], comment: "A counter of the total number of jobs sidekiq executed."
	counter :jobs_success_total, tags: %i[queue worker], comment: "A counter of the total number of jobs successfully processed by sidekiq."
	counter :jobs_failed_total, tags: %i[queue worker], comment: "A counter of the total number of jobs failed in sidekiq."
	gauge :jobs_waiting_count, tags: %i[queue], comment: "The number of jobs waiting to process in sidekiq."
	gauge :active_workers_count, tags: [], comment: "The number of currently running machines with sidekiq workers."
	gauge :jobs_scheduled_count, tags: [], comment: "The number of jobs scheduled for later execution."
	gauge :jobs_retry_count, tags: [], comment: "The number of failed jobs waiting to be retried"
	gauge :jobs_dead_count, tags: [], comment: "The number of jobs exceeded their retry count."
	gauge :active_processes, tags: [], comment: "The number of active Sidekiq worker processes."
	gauge :queue_latency, tags: %i[queue], comment: "The queue latency, the difference in seconds since the oldest job in the queue was enqueued"
	gauge :running_job_runtime, tags: %i[queue worker], aggregation: :max, unit: :seconds,
	comment: "How long currently running jobs are running (useful for detection of hung jobs)"
	histogram :job_latency, comment: "The job latency, the difference in seconds between enqueued and running time",
	unit: :seconds, per: :job,
	tags: %i[queue worker],
	buckets: LONG_RUNNING_JOB_RUNTIME_BUCKETS
	histogram :job_runtime, comment: "A histogram of the job execution time.",
	unit: :seconds, per: :job,
	tags: %i[queue worker],
	buckets: LONG_RUNNING_JOB_RUNTIME_BUCKETS

README lists metrics here: https://github.com/yabeda-rb/yabeda-sidekiq/blob/91c8f4ed23a2687b396ac64add8236f3ed16f0cc/README.md#metrics