Allow setting an avatar image for the bot's account

Cargo.lock

@@ -371,6 +371,9 @@ dependencies = [
  "http",
  "log",
  "matrix-sdk",
+ "mime",
+ "mime-sniffer",
+ "mime_guess2",
  "quick-xml",
  "regex",
  "reqwest",
@@ -1826,12 +1829,34 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "mime-sniffer"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6b8b2a64cd735f1d5f17ff6701ced3cc3c54851f9448caf454cd9c923d812408"
+dependencies = [
+ "mime",
+ "url",
+]
+
 [[package]]
 name = "mime2ext"
 version = "0.1.54"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cbf6f36070878c42c5233846cd3de24cf9016828fd47bc22957a687298bb21fc"
 
+[[package]]
+name = "mime_guess2"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1706dc14a2e140dec0a7a07109d9a3d5890b81e85bd6c60b906b249a77adf0ca"
+dependencies = [
+ "mime",
+ "phf",
+ "phf_shared",
+ "unicase",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"
@@ -2034,6 +2059,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "syn",
+ "unicase",
 ]
 
 [[package]]
@@ -2043,6 +2069,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "67eabc2ef2a60eb7faa00097bd1ffdb5bd28e62bf39990626a582201b7a754e5"
 dependencies = [
  "siphasher",
+ "unicase",
 ]
 
 [[package]]