Log Message:
prometheus: update to 2.28.0

While here try to make updates less painful for pkgsrc developers
by automating some of the manual steps.

2.28.0 / 2021-06-21
  [CHANGE] UI: Make the new experimental PromQL editor the default.
  [FEATURE] Linode SD: Add Linode service discovery.
  [FEATURE] HTTP SD: Add generic HTTP-based service discovery.
  [FEATURE] Kubernetes SD: Allow configuring API Server access via a kubeconfig file.
  [FEATURE] UI: Add exemplar display support to the graphing interface.
  [FEATURE] Consul SD: Add namespace support for Consul Enterprise.
  [ENHANCEMENT] Promtool: Allow silencing output when importing / backfilling data.
  [ENHANCEMENT] Consul SD: Support reading tokens from file.
  [ENHANCEMENT] Rules: Add a new .ExternalURL alert field templating variable, \ 
containing the external URL of the Prometheus server.
  [ENHANCEMENT] Scrape: Add experimental body_size_limit scrape configuration \ 
setting to limit the allowed response body size for target scrapes.
  [ENHANCEMENT] Kubernetes SD: Add ingress class name label for ingress discovery.
  [ENHANCEMENT] UI: Show a startup screen with progress bar when the TSDB is not \ 
ready yet.
  [ENHANCEMENT] SD: Add a target creation failure counter \ 
prometheus_target_sync_failed_total and improve target creation failure \ 
handling.
  [ENHANCEMENT] TSDB: Improve validation of exemplar label set length.
  [ENHANCEMENT] TSDB: Add a prometheus_tsdb_clean_start metric that indicates \ 
whether a TSDB lockfile from a previous run still existed upon startup.
  [BUGFIX] UI: In the experimental PromQL editor, fix autocompletion and parsing \ 
for special float values and improve series metadata fetching.
  [BUGFIX] TSDB: When merging chunks, split resulting chunks if they would \ 
contain more than the maximum of 120 samples.
[BUGFIX] SD: Fix the computation of the prometheus_sd_discovered_targets metric \ 
when using multiple service discoveries

2.27.0 / 2021-05-12
  [FEATURE] Promtool: Retroactive rule evaluation functionality.
  [FEATURE] Configuration: Environment variable expansion for external labels. \ 
Behind --enable-feature=expand-external-labels flag.
  [FEATURE] TSDB: Add a flag(--storage.tsdb.max-block-chunk-segment-size) to \ 
control the max chunks file size of the blocks for small Prometheus instances.
  [FEATURE] UI: Add a dark theme.
  [FEATURE] AWS Lightsail Discovery: Add AWS Lightsail Discovery.
  [FEATURE] Docker Discovery: Add Docker Service Discovery.
  [FEATURE] OAuth: Allow OAuth 2.0 to be used anywhere an HTTP client is used.
  [FEATURE] Remote Write: Send exemplars via remote write. Experimental and \ 
disabled by default.
  [ENHANCEMENT] Digital Ocean Discovery: Add __meta_digitalocean_vpc label.
  [ENHANCEMENT] Scaleway Discovery: Read Scaleway secret from a file.
  [ENHANCEMENT] Scrape: Add configurable limits for label size and count.
  [ENHANCEMENT] UI: Add 16w and 26w time range steps.
  [ENHANCEMENT] Templating: Enable parsing strings in humanize functions.
  [BUGFIX] UI: Provide errors instead of blank page on TSDB Status Page.
  [BUGFIX] TSDB: Do not panic when writing very large records to the WAL.
  [BUGFIX] TSDB: Avoid panic when mmaped memory is referenced after the file is \ 
closed.
  [BUGFIX] Scaleway Discovery: Fix nil pointer dereference.
  [BUGFIX] Consul Discovery: Restart no longer required after config update with \ 
no targets.