Explore: Logging label filtering

removed extra whitespace

added google_tag_manager_id from defaults.ini

removed extra whitespace

Update export_import.md

Grafana v5.3.4 shows a new checkbox in the export modal "Export for sharing externally". If the checkbox is not checked then the "__inputs" section wont be included into the exported JSON file, would be great to add that note into the documentation for others to avoid confusions.

- adds a custom label renderer to Logs viewer in Explore
- labels are no longer treated as strings, they are passed as parsed objects to the log row
- label renderer supports onClick handler for an action
- renamed Explore's `onClickTableCell` to `onClickLabel` and wired up log label renderers
- reuse Prometheus `addLabelToSelector` to modify Logging queries via click on label
- added tests to `addLabelToSelector`, changed to include the surrounding `{}`
- use label render also for common labels in the controls panel
- logging meta data section has now a custom renderer that can render numbers, strings, and labels
- style adjustments

Logging: fix query parsing for selectors with multiple labels

- simplify selector parsing
- added tests

Explore: Scan for older logs

fix elastic ng-inject issue in query editor

Sometimes log streams dont return any lines for the given range. Would be great to automate the search until some logs are found.

- Allow Explore to drive TimePicker via ref
- Show `Scan` link in Logs when there is no data
- Click on `Scan` sets Explore into scanning state
- While scanning, tell Timepicker to shift left
- TimePicker change triggers new queries with shifted time range
- Remember if query transaction was started via scan
- keep scanning until something was found
- Manual use of timepicker cancels scanning

Explore: Filter logs by log level

Remove confusing <> from variable intro

The existing intro makes it look like you should use `$<varname>` to refer to a variable. That of course is incorrect, and you should use `$varname`. In my experience using the <> marker around variable names should only be used when there isn't something else explicit to set it off. In this case we have `$`. Below, you can see the <> are also not used, because we have the `[[]]` to set it off. The inconsistency is confusing.

Related to #14182

chore: correct pause-all-alerts auth in docs

log the actual error if failing to update alert data

docs: what's new in v5.4

Explore: Fix JS error when switching between 2 prometheus datasources

- since the DataQuery rewrite, Explore starts by submitting its queries (Explore cant know if the queries are emtpty)
- The datasource intercepts an empty query and returns an empty list of time series, and also no table for the table query.
- The query hinter then received no series to analyse and was not guarding against this.
- This PR adds this guard.

Sort Prometheus range suggestions by length

- add `onToggleSeries` to Explore Graph props
- toggling a Logging Graph series from the legend propagates its hidden series to Logs
- Logs translates hidden series alias to LogLevels
- Logs filters out hidden log levels

Regression: fix handle of elasticsearch 6.0+ version

Explore: make query field suggestions more robust

- drop invalid history items
- make highlighter more robust by defaulting to empty string on text to highlight