Log Message:
prometheus: update to 2.26.0

Prometheus is now built and supporting Go 1.16.
Note that from this release Prometheus is using Alertmanager v2 by default.
[CHANGE] Alerting: Using Alertmanager v2 API by default.
[CHANGE] Prometheus/Promtool: As agreed on dev summit, binaries are now printing \ 
help and usage to stdout instead of stderr.
[FEATURE] Remote: Add support for AWS SigV4 auth method for remote_write.
[FEATURE] Scaleway Discovery: Add Scaleway Service Discovery.
[FEATURE] PromQL: Allow negative offsets. Behind \ 
--enable-feature=promql-negative-offset flag.
[FEATURE] experimental Exemplars: Add in-memory storage for exemplars. Behind \ 
--enable-feature=exemplar-storage flag.
[FEATURE] UI: Add advanced auto-completion, syntax highlighting and linting to \ 
graph page query input.
[ENHANCEMENT] Digital Ocean Discovery: Add __meta_digitalocean_image label.
[ENHANCEMENT] PromQL: Add last_over_time, sgn, clamp functions.
[ENHANCEMENT] Scrape: Add support for specifying type of Authorization header \ 
credentials with Bearer by default.
[ENHANCEMENT] Scrape: Add follow_redirects option to scrape configuration.
[ENHANCEMENT] Remote: Allow retries on HTTP 429 response code for remote_write. \ 
Disabled by default. See configuration docs for details.
[ENHANCEMENT] Remote: Allow configuring custom headers for remote_read. See \ 
configuration docs for details.
[ENHANCEMENT] UI: Hitting Enter now triggers new query.
[ENHANCEMENT] UI: Better handling of long rule and names on the /rules and \ 
/targets pages.
[ENHANCEMENT] UI: Add collapse/expand all button on the /targets page.
[BUGFIX] TSDB: Eager deletion of removable blocks on every compaction, saving \ 
disk peak space usage.
[BUGFIX] PromQL: Fix parser support for special characters.
[BUGFIX] Rules: Update rule health for append/commit fails.