LogQL line format: Add Entry variable to template

[riptl]

Is your feature request related to a problem? Please describe.

The templates in line_format only have labels as inputs. They are missing the log entry.
This makes it impossible to do string interpolation involving the log entry.

Describe the solution you'd like

Add the .Entry variable to line_format templates containing the log entry, like was done in #2105 for promtail templates.

Describe alternatives you've considered
none

Additional context
none

[nvtkaszpir]

this can be now mitigated by extra query filter chains:

{namespace="my-namespace"} | regexp "(?P<msg>.*)" | line_format "{{.custom_label}} {{ .msg }}"

in short msg will match everything in message, but there should be nicer way to do it.

[pgassmann]

instead of the regex, the pattern matcher works too.
| pattern "<MESSAGE>" | line_format "{{.custom_label}} {{ .MESSAGE }}"

[jeschkies]

@terorie would that suffice?