* vendor: Update prometheus/tsdb

This time, properly
Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

* release 2.4.2
Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

Fixes #4597
Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

Signed-off-by: NGoutham Veeramachaneni <gouthamve@gmail.com>

Signed-off-by: NBrian Brazil <brian.brazil@robustperception.io>

Signed-off-by: NBrian Brazil <brian.brazil@robustperception.io>

Signed-off-by: NFabian Reinartz <freinartz@google.com>

Signed-off-by: NFabian Reinartz <freinartz@google.com>

Signed-off-by: NKarsten Weiss <knweiss@gmail.com>

This adds support for basic authentication which closes #3090

The support for specifying the client timeout was removed as discussed in https://github.com/prometheus/common/pull/123. Marathon was the only sd mechanism doing this and configuring the timeout is done through `Context`.

DC/OS uses a custom `Authorization` header for authenticating. This adds 2 new configuration properties to reflect this.

Existing configuration files that use the bearer token will no longer work. More work is required to make this backwards compatible.

Signed-off-by: NGoutham Veeramachaneni <cs14btech11014@iith.ac.in>

If the other Prometheus has an external label that matches that of
the Prometheus being read from, then we need to remove that matcher
from the request as it's not actually stored in the database - it's
only added for alerts, federation and on the output of the remote read
endpoint.
Instead we check for that label being empty, in case there is a time
series with a different label value for that external label.

Signed-off-by: NGoutham Veeramachaneni <cs14btech11014@iith.ac.in>

Signed-off-by: NGoutham Veeramachaneni <cs14btech11014@iith.ac.in>

Apparently, a decision was made at some point to only use the v prefix
in tags and similar contexts where other things can appear. There was a
vote to stick to that decision. For more information, read
https://github.com/prometheus/prometheus/pull/2743.

This reverts commit 5405a472.