Patch HTTPClient to accept socket_connect_timeout

[philippthun]

Monkey patch HTTPClient to accept socket_connect_timeout as optional configuration. If set, it is used as connect_timeout parameter when creating a TCPSocket.

Set the socket_connect_timeout in Diego::Client to (overall) connect_timeout / 2.

Add test to ensure that the httpclient version is not updated without revisiting the monkey patch.

Background information

ℹ️ Use case: Mitigates the risk of Runner is unavailable and Stager is unavailable errors during a cf push when the client is unable to reach a bbs instance.

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❌ First, discarded solution proposal: #3002

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✔️ Second, merged solution proposal: #3048

💥 Issues caused by #3048

• After recent changes in bbs selection process, passive nodes randomly causing errors #3109
• /v2/spaces/<spaceguid>/summary produces "-1" running_instances for all apps, instead of actual # instances #3112
• sporadically failing sync-integration-tests

ℹ️ Root cause: Net::HTTP and altered Diego::Client implementations are not thread-safe.

🔄 Revert PR: #3113

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✔️ Third, merged solution proposal: #3170

💩 Issues caused by #3170

• cc-unit-tests failing (Concourse)

ℹ️ Root cause: Concourse executes the unit tests with Ruby 3.1.3 (as opposed to the version 3.1.2 specified in .ruby-version) which includes a newer Net::HTTP version that reverted the usage of the Socket.tcp's connect_timeout option (see ruby/net-http#74).

🔄 Revert PR: #3171

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• I have made this pull request to the main branch

• I have run all the unit tests using bundle exec rake

• I have run CF Acceptance Tests

[philippthun]

@johha and me prepared a local test environment to simulate an unresponsive bbs server and ran tests with different HTTP clients:

HTTP client	10 sequential pings	50 parallel threads	Notes
httpclient	❌ fails	n/a	current implementation
httpclient + monkey patch	✅ succeeds	✅ succeeds	set connect_timeout on TCPSocket
net_http (only v0.2.x)	✅ succeeds	❌ fails
net_http_persistent (only with net_http v0.2.x)	✅ succeeds	✅ succeeds	pool_size: 50
net_http (other versions)	❌ fails	n/a
http.rb	❌ fails	n/a