Built in profiling capabilities with excimer

[juliusknorr]

This PR adds simple profiling capabilities that can be turned on with config.php options. This is similar to what sentry already offers but in most setups that need debugging installing sentry is not something that can be achieved on short notice.

Blackfire can already be used but requires a subscription and can not sample without an extra plan.

It has two operation modes:

1. Profile a single request

This can be either enabled for all requests (very heavy) or when sending a configured secret along the request. The files are stored using the date and request id to find them more easily.

# Set this in config php
  'profiling.secret' => 'secret',
# Send a curl request with the secret
$ curl 'https://nextcloud.local/index.php/login?profile_secret=secret'
# See the file in /tmp/profile-* 

3. Samping the request at a configured rate

The request will be sampled to a file that can be rotated in a custom amount of time (e.g. every hour or every 5 minutes)

# Set this in config.php
  'profiling.sample' => true,
  'profiling.sample.rate' => 0.5,
# Send some requests and see the sample profile at /tmp/sample-*

The files will be just written to a configurable path (/tmp by default)

Just a quick implementation for now, this could become more sophisticated, but I used this a couple of times already as a code dump in config.php and it is really useful

https://github.com/jlfwong/speedscope can be used to plot colorful graphs

[ChristophWurst]

Really good stuff 🙏 It's nice to have this built into Nextcloud