feat: parse pem certificates

[LeoBorai]

Revisits TLS and HTTPS serving. Adds support for PEM files loading.

[LeoBorai]

@stackinspector I have been checking on the TLS certificates issue as you suggested on #128.
I did update the rustls PEM file parser crate and also ensure the buffer loads bytes from file as expected.

I tested the HTTP Server using certificates generated by mkcert,
here is the step by step on how I got it running.

1. Create certificates with mkcert as follows:

mkcert -cert-file tmp/local.test-http-server.com.crt -key-file tmp/local.test-http-server.com.key local.test-http-server.com

2. Then added local.test-http-server.com to my /etc/hosts file:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1             localhost

# Added by User
127.0.0.1       local.test-http-server.com

3. Finally run the HTTP Server

cargo run -- --tls  --tls-cert ./tmp/local.test-http-server.com.crt --tls-key ./tmp/local.test-http-server.com.key --verbose --logger --tls-key-algorithm pkcs8 --proxy https://example.com

4. Open your favorite browser and visit https://local.test-http-server.com:7879, you must see example.com through the proxy.

Please let me know any questions! I'm glad to help!

[LeoBorai]

@stackinspector given that now we are loading the PEM files accordingly Im merging this.
Please let me know any issues you have!