Added support for Open Telemetry

[ezimuel]

Following the guideline reported here, I added the support for Open Telemetry in Transport::sendRequest() function.

This PR adds an elasticsearch-api tracer using the Globals::tracerProvider() of the Open Telemetry API for PHP.
In the Transport::sendRequest() I created a span with the following attributes:

http.request.method
url.full
server.address
server.port

I also added an optional parameter to the Transport::sendRequest() function as follows:

public function sendRequest(RequestInterface $request, array $opts = []): ResponseInterface

The $opts array contains additional OTel attributes that can be passed at runtime. This array will be used to fullfill the specific Elasticsearch OTel attributes like:

db.operation.name
db.elasticsearch.path_parts.<key>
db.query.text

The complete list of Elasticsearch attributes is reported here.

This PR solves #24

[picandocodigo]

LGTM 👍

[picandocodigo]

These (email, tel, phone) are not present in the Ruby version. Are these standard or did you add them? Maybe I should add them too for consistency across our clients.

[ezimuel]

I added since I think they can be considered sensitive information. But we also offer the possibility to customize it using the ENV variable, i.e. OTEL_RUBY_INSTRUMENTATION_ELASTICSEARCH_SEARCH_QUERY_SANITIZE_KEYS.