Add status endpoint to list the available endpoints

[zalegrala]

Here we include an /admin endpoint that will print all the available endpoints and the regex that will route to the endpoint.

+------------------------------------------+------------------------------------------------+
| NAME                                     | REGEX                                          |
+------------------------------------------+------------------------------------------------+
| /api/echo                                | ^/api/echo$                                    |
| /api/search                              | ^/api/search$                                  |
| /api/search/tag/{tagName}/values         | ^/api/search/tag/(?P<v0>[^/]+)/values$         |
| /api/search/tags                         | ^/api/search/tags$                             |
| /api/traces/{traceID}                    | ^/api/traces/(?P<v0>[^/]+)$                    |
| /config                                  | ^/config$                                      |
| /debug/pprof                             | ^/debug/pprof                                  |
| /flush                                   | ^/flush$                                       |
| /ingester/ring                           | ^/ingester/ring$                               |
| /memberlist                              | ^/memberlist$                                  |
| /metrics                                 | ^/metrics$                                     |
| /querier/api/search                      | ^/querier/api/search$                          |
| /querier/api/search/tag/{tagName}/values | ^/querier/api/search/tag/(?P<v0>[^/]+)/values$ |
| /querier/api/search/tags                 | ^/querier/api/search/tags$                     |
| /querier/api/traces/{traceID}            | ^/querier/api/traces/(?P<v0>[^/]+)$            |
| /ready                                   | ^/ready$                                       |
| /services                                | ^/services$                                    |
| /shutdown                                | ^/shutdown$                                    |
| /status                                  | ^/status$                                      |
+------------------------------------------+------------------------------------------------+

API documentation: https://grafana.com/docs/tempo/latest/api_docs/

Which issue(s) this PR fixes:
Fixes #632

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[annanay25]

Nice work.

Even though I feel the addition of api docs (https://grafana.com/docs/tempo/latest/api_docs/) has depreciated this endpoint, its still nice to have. Some nits:

• Can we add a "table header"? It might be confusing to just see the regex
• Can we add a line at the end pointing to the api docs for further info?

[joe-elliott]

Should we call this /admin when all it does is print out http endpoints? I feel like we should consolidate here. Perhaps /services and this functionality could be combined into /status or /info and we could continue fleshing it out with info about the running process.

Possibly even support some basic arguments (otherwise dump everything):
/status?config
/status?runtime_config
/status?services
/status?endpoints

[zalegrala]

Great suggestions, thanks for the review. Do we want a table printed here, or something machine consumable. I feel like if I were to call something on /status I might expect JSON. We could still keep a docs link in the payload too But if we're looking for something that folks can reference with eyeballs easier, then perhaps just a table.

[zalegrala]

I've made some updates here and set us up to add more query params later on a /status endpoint, and the data is now written as a table.

[zalegrala]

I'll update the docs page too.

[achatterjee-grafana]

Added doc review.