Remove dependency on sentry package?

[grzuy]

Motivated in part by #39 (comment).

Currently we're calling two function from sentry package.

• In Event.ex https://github.com/mimiquate/tower_sentry/blob/main/lib/tower_sentry/sentry/event.ex#L16
• In Client.ex https://github.com/mimiquate/tower_sentry/blob/main/lib/tower_sentry/sentry/client.ex#L7

Would be interesting at least seeing a unfinished draft of some pieces of the implementation needed to replace Sentry.Event.create_event and Sentry.Client.send_event.

First draft doesn't need to have feature parity at all with what currently create_event and send_event have which is feature heavy.

Worth trying something super simple and slim at first:

• for the create event alternative, an implementation that just barely builds the simplest envelope with just one event payload
• for the send event alternative, a simple implementation using httpc (similar to other tower reporters, see below) that just sends the payload to sentry using configured DSN

Maybe it's not too much...

What's to gain:

• Less confusion when configuring :tower_sentry (see Confusion about :tower_sentry vs :sentry config #39)
• Remove risk of future incompatibility or changes in these sort of "private functions" we're depending on
• No longer need to test and support multiple version of a dependent package
• Not depend on an external dependency from which we're using a subset of all it's code.

Test cases should "mostly" continue to be green/pass with the changed/refactored code, as they test the sent payload structure which I guess would be similar.

Other reporter's implementations:

• Building payload:

  • TowerBugsnag.Bugsnag.Event
  • TowerRollbar.Rollbar.Item

• Clients sending payload:

  • TowerBugsnag.Bugsnag.Client
  • TowerRollbar.Rollbar.Client